We are 2 adults travelling with a baby, and have heavy luggage. I'm discouraged by low cost airlines. Easyjet was the cheapest one but Im a little bit concerned about the strict rules and the airport where the departure is (schonefeld). By bus Im corcerned if the booster seat is a must, as we dont have any and if you buy a ticket on the web it says is an obligation to have one on your own if you decide to travel with a baby. However, we travelled from liubliana to zagreb without any problem. Perhaps in GErmany are more strict. Finally by train, is way too expensive and it would be worst if I let time go by.
Well, thanks for your attention!
Although by train is not the most affordable, it is the most convenient for travelling with a baby. No infant seats are required and there is plenty of room for both of you to walk about the aisles with the baby. The baby is also much less likely to get motion sickness or a bad earache from the cabin pressure. It may be worthwhile to spend a bit more money to travel by rail for those reasons.
You can also have a look at flixbus.de to check for buses from Berlin to Amsterdam.
goeuro.com should deliver the best survery.
Rent a car.
The Dutch Railways have a ticketsale to Berlin tomorrow. Maybe returns are cheap too. Prices start at €29 and the sale starts at 9am till midnight. www.nsinternational.nl
If you want to fly you could try Transavia. Besides to Amsterdam they also fly to Rotterdam, which isn't that far from Amsterdam. Tickets might be cheaper there.
Maybe carpooling, try www.blablacar.com
Compare different possibilities at www.goeuro.com
It may be that Flixbus is the cheapest, but this is definetly not always the case. Sometimes travelling with Deutsche Bahn is much cheaper, and, of course, much more comfortable. But you have to book in advance to get the cheaper tickets.