Activities during reunion in santa cruz

Absolutely check out the Santa Cruz Beach Boardwalk and Santa Cruz Beach.  The boardwalk has all the stuff you need from games to junk food and rides from spinny to rollar coasters. (The Giant Dipper is historical and still fun after eons... it was my first coaster.)

What's great is that the boardwalk is on the beach, so if you and the kids want to get away from the noise and rides and play in the waves you can and there are places to shower off a bit.

Dharmin's right.  The The Mystery Spot is cool for younger kids.  I always went there growing up.

For dinner, my favorite is Vasili's Greek Restaurant .  The food is amazing and I've driven down from the Bay area just for dinner. So good.

I guess when I think "dad's," I think beer, and Santa Cruz has some fun local breweries.  Check out the Seabright Brewery or the Santa Cruz Mountain Brewing.  These are just two of about six places, so do a quick search online and you'll be able to make your own beer map and have fun.

There are also a lot of outdoor things.  Try surfing (Santa Cruz is known for that) or take a ride on one of many bike trails.  It's a great place to explore.  Dads AND kids will like Henry Cowell Redwoods State Park .  It's beautiful, great for hiking and riding, and not far from the city.

For the family, beyond the obvious fun at the Santa Cruz Beach Boardwalk, I think Natural Bridges State Beach is the best in the area. It has a visitor's center and lots of interesting things to see. For the guys, in addition to the Santa Cruz Mountain Brewing noted in another answer, there is a new place literally across the alley called the West End Tap & Kitchen. IMHO better beer selection, plus great food. But they don't make beer on the premises. On the East side at the end of Seabright Ave. is the alway excellent Seabright Brewery. Try the fantastic Calamari sandwich.

The Santa Cruz Beach Boardwalk is a nice and relaxing place. You will find crowds during the weekend. Lot of fun rides for kids. 

Also the The Mystery Spot is a great attraction if you have never been there. 

I'm a vegetarian guy so my food recommendation would be limited to garlic fries on the boardwalk ;)

Santa Cruz Beach Boardwalk is definitely worth a visit! So much fun to just hang out at the beach and try some rides.