(congrats!)

First, go in the earliest part of autumn that you can.  It doesn't get crazy cloudy/drizzly 'till later in the fall (usually) but no harm in stacking the deck.  The NW colors aren't very dramatic compared to the east coast and they often don't show up until the nasty weather does.

Where to stay
If you're going to splurge, the Edgewater Hotel is a great location and literally hangs over the water.  It's walkable to the  Olympic Sculpture Park and  Pike Place Market.  There are also a few really nice hotels on 5th/6th...  But those can be a bit of a hike up the hill from Pike Place Market.  AirBnB might be worth a look too (but you should have a guide-- downtown neighborhoods are safe but certain ones can be dirty/noisy).

Landscapes
For otherworldly northwestern rainforest feel right in the city, you can't beat  Schmitz Preserve Park in West Seattle.  UW sends botany students here-- it's the closest example of old-growth in Seattle.  You could take the water taxi over to West Seattle ($3.50).  On the other side is a Hawaiian/Korean fusion place that is awesome ( http://marinationmobile.com/ma-kai ) and a free shuttle to Alki Beach (a great place to run, see the Seattle skyline, and wander up into Schmitz).

Golden Gardens is also a pretty park up near Ballard.

Gasworks Park Marina is a fun park to see Lake Union.  You can drive, or if you're feeling ambitious you can rent an electric boat ( http://www.theelectricboatco.com/ ) with a bag full of food/drink and see it from the water.   Agua Verde Paddle Club ( http://aguaverde.com/ ) has a dock.  You can (if you do the electric boat) dock there for lunch or (if you drive) you could rent a kayak there.

There are more landscapes outside of Seattle.   Cave B (http://www.cavebinn.com/ ) is built organically in/around the side of the columbia river gorge.  Gorgeous country with a winery on site.  Leavenworth is a hilarious bavarian themed town worth gorgeous landscapes around it.  The San Juan Islands are peerless.  You could head down to Mt. Ranier.  All depends on how far you feel like driving or whether you want to stay in town.

Food
It looks like you're from LA-- Seattle is quite compact compared to what you're used to.  Any restaurant you find on Yelp/Urbanspoon will be within a 20m drive.  I'm running low on time, but  Lark and  Matt's in The Market are two fine dining favorites of mine (ask for a view seat at Matt's and make reservations well in advance).  I'd favor www.urbanspoon.com over Yelp - the founders are foodies from Seattle, so it's pretty solid there.

Was recently in Seattle, there are some really amazing places to eat in the  Ballard Neighborhood

1.  The Walrus and the Carpenter - known for their raw oysters but their cooked and non-seafood options are amazing as well. They don't take reservations so plan on getting there earlier in the evening to secure a table.

2.  Bastille Cafe & Bar - just a few steps from the Walrus and the Carpenter. As you might guess from the name this restaurant serves up French cuisine , paired with a lively ambience and a rustic but refined decor.

3.  Cupcake Royale and Verite Coffee- multiple locations, but I went to one in Ballard. Some of the best cupcakes I've ever had with a perfect balance of moisture and sweetness.

4. Hot Cakes Molten Chocolate Cakery - another great dessert place, they feature delicious "adult" shakes that your husband might enjoy.

Take a trip (about 2 hours) to Leavenworth (Washington) and explore an amazing bavarian town.  There is plenty to do--including wine and chocolate tasting and it's absolutely beautiful.  If you time it right, you can even be there during their annual Oktoberfest!

Congratulations on the little one, and good choice on Seattle!  Love that city :)

I've always stayed with a friend, so I don't have hotel recommendations, but said friend was a chef at the Lark that Tony W. mentioned for many years, so whenever I visited, memorable food adventures were had!  I'll try to narrow it down to my top 10...

• How To Cook A Wolf -- fond memories of coming to this place when it had just opened a few years ago.  It's where I fell in love with food, and I even got to meet chef Ethan Stowell that day!  At the time, I think he had one other awesome high end restaurant and this was his fun project.  He's gone on to closing that restaurant and opening a few other good ones, too.  His specialty seems to be modern Italian-American.  I like this one because it's in the not-very-bustling Queen Anne neighborhood. ...But that doesn't mean that there wouldn't be a line for this place!
  
• Tavolata -- Ethan Stowell's newer Italian place, it's hip and trendy.  They have small-medium dishes that are meant to be shared family style so everyone gets a little taste of everything, or you could just do drinks there at the bar (can get food at the bar as well).
  
• The Coterie Room -- love this place.  Looks super fancy, but I had apps and drinks at the bar and the bartender was a hoot, plus they serve fun foods, like pork skin cracklings with cheese sauce.  It was like fancy nachos.  Also, on the menu, there's an option that says something like "Send a 6-pack of beer to the kitchen staff" for $10.
  
• La Bête is awesome.  Some guys who used to work at Lark left to start this place.  Very whimsical and creative restaurant.  Their rabbit mousse was amazing.
  
• Le Pichet -- Gotta come here.  Traditional French fare that has become a Seattle institution.  Tiny, charming little spot.  Open late night.
  
• Cafe Presse -- This is Le Pichet's sister restaurant.  More diner style than Le Pichet, but serves a mean croque madame and croque monsieur with bottomless coffee.
  
• Local 360 -- If you like oysters, you can celebrate being able to eat them again here! Great oyster happy hour, plus other grub, like mac n cheese and burgers, plus awesome drinks in a pub'ish environment.  Everyone who I've ever recommended this to has ended up going back multiple times during a trip because it's such a good deal for such good food.
  
• Quinn's Pub -- Nothing fancy, this is a straight up pub.  This is where my chef friend would often meet up with chefs from other restaurants after work to decompress.  Great food and drinks.
  
• Little Uncle Seattle -- This one's just fun.  It's a Thai food stand that serves both traditional Thai fare plus a few experimental ones.  I think the man who opened this up also used to work at Lark.  Best khao mun gai that I've ever eaten out of butcher paper and the pork cheek buns were tasty, too.
  
• Lark -- This just goes without saying.
  

To really experience Washington's green-ness, I always suggest that people go up to Whidbey Island.  It's off the beaten path because it's not a place that most people trek to when they say that they're visiting Seattle.  It's seriously one of my favorite places ever and I'm sure will be beautiful in the fall.  It's pretty remote and a great place to really get away for a bit while still being relatively close to Seattle.  It's just a 1 hour ride up to the port plus about 30 minutes to ferry over.  If you want more info, I wrote more about it here, about how to get there and what to see.

Have fun!

If you like Hawaiian food, you should take the  King County Water Taxi to  Marination Ma Kai in West Seattle. It's a casual sit-down restaurant with the best shave ice and Hawaiian food outside of Hawaii. : ) The patio has a bar and a great view. It's currently my favorite place in Seattle. : )

After that, you can walk to  Alki Beach Park and enjoy the views and shops along the way. Get some wine and have a picnic! 

Have fun!

Have you been to Bainbridge Island? It's sorta like the love child of Cape Cod and Brooklyn: a teeny tiny city on an island with lots of organic food, farmers markets and boutique restaurants. There's a Zagat 5-star place over there called Hitchcock Restaurant that I pretty much ate out of house and home and a great bakery called Blackbird Bakery with gluten-free options and a million types of organic, locally-sourced coffee beans (oh, Seattle), as well as several wineries. Plus the Bainbridge Island Ferry is about 30 minutes long and you can take your car on it, so it can be a weekend trip or a half-day trip.

If your open to going outside of the city. It would be worth checking out the Salish Lodge & Spa in Snoqualmie. 

http://www.salishlodge.com

For a nice hotel,  Pan Pacific Seattle is a solid family/business hotel in the South Lake Union neighborhood... walking distance to lots of stuff, great food, streetcar, downtown, parks, etc.

As far as good food goes, these are some of my favorites...

• Sitka & Spruce: My friend Matt Dillon is an amazing Beard-winning chef here. So so good. He's one of Seattle's best.  Moroccan influenced Northwest cuisine. Chill vibe, foodies delight in this.
  
• The Corson Building: Another great restaurant by Matt Dillon. Family style dining.  One or two seatings nightly.
  
• Madison Park Conservatory: Another amazing place to dine and is one of my top 3 in seattle. Featured by the NY Times, Chef's Cormac & Zoe are tops, service, food is world class. Foodies will flip over this..  Not to miss.  Say hi to the chefs.  
  
• La Bête: Yummy French bistro on west slope of Capitol Hill Neighborhood. Best surprise is the pop-up Thai night that's going on there now every Monday....amazing.
  
• Spring Hill Restaurant & Bar: In West Seattle, but worth the drive/cab. Chef Mark Fuller is genius - Food & Wine Magazin top 10 chefs in the country 2009 or 2010...
  
• Staple and Fancy Mercantile: Italian inspired, nw roots food by great seattle chef Ethan Stowell. great neighborhoody spot, edge of hipster ballard, right next door to  The Walrus and the Carpenter.
  
• How To Cook A Wolf: Amazing pasta.  Another Ethan Stowell place.  No reservations so show up early.
  
• Cantinetta: Another great neiborhood italian joint. Great eats/people/wine. Avocado salad is simple and mind blowingly good.
  
• Book Bindery: Tasty eats in an out of the way location on the canal.
  
• Canlis Restaurant: Seattle's most classic mid-century restaurant. High end, great food, new vision from younger generation of Canlis family. Dinner guest ranges from 20-70.
  

For things to do, taking the  Bainbridge Island Ferry is a must do in Seattle, but only if it's sunny.  Of course, there's the  Space Needle. love this icon. 8th most photographed thing in the world! It's touristy - but its actually really cool. I just took my nephew after not having been there for a decade or more. Sorta spendy, but worth it.  The restaurant up top has done a full 180 and is actually quite good.  Another place with a unique view is the observation deck at  Smith Tower.

If you like museums, The newly refurb-ed Seattle Art Museum is great.  Getting better every year.... the remodel is substantial. Check out the sculpture park on elliott bay too - also part of SA (Go SAM!).  The  Experience Music Project is a music museum.  Cool spot even if touristy... If you like architecture, check out the  Seattle Public Library - Central Library. great architecture - rem koolhaas. make sure to go INSIDE. stunning