Hi A.,
We lived in Germany for a few years, so we've done our fair share of flying recently.
Typically you can bring on liquids for children, but they will be tested. I would bring the unmixed formula, and then buy water at the airport to mix.
Just a tip on traveling with little ones. Pack as light as you can. It's tough keeping kids and all their gear in tow through an airport.
Also, strollers....can be checked at the gate. However, depending on the size, you may or may not be able to get it at the destination gate. They may actually CHECK it at the gate instead of just putting it in the hold. Ask what the policy is when you check in.
There are typically changing tables in the walls in the bathroom. The bathrooms are small on the plane...but totally doable. I've done a complete blowout change in one of those bathrooms! ;-)
Children under the age of 2 can sit on your lap. Just keep in mind... they will be on your lap for that time. It can be tough if it's a long flight. We've done both. Children over 2, need their own seat. They aren't REQUIRED to have the carseat on the plane, but I will say, now that my daughter is almost 2, the next time we fly, I will be bringing it. Kids are used to car seats. The last time we flew, my daughter was 10 months old. She had her own seat, no carseat. Talk about WIGGLE issues! oiy. Next time... car seat.
Ok, that's what I have.
Have a great trip!