As an American living in Stuttgart I'm well aware of the various American items that can't be purchased in Germany. However, most of the ones I miss and bring back from trips to the US are not appropriate for gifts. Some more appropriate things you might consider which I like are Turtles candy, salt water taffy, atomic fireballs/Louisiana fire crackers (which my German wife loves), and whole smoked Alaskan salmon in foil (available through members-only large discount grocery stores). Although I buy them for myself as they can be carried without melting, PayDay candy bars rapidly disappear because my wife loves them. Note, that the items I've listed have little or no chocolate in them, as German tastes tend to differ quite significantly from American ones, with Americans prefering much sweeter things.

Otherwise, I think its always nice to give things that are related to where you're from, as it is a more personal touch.

Liquid cheese in bottles you can't get anywhere in Germany, so it would be a very freaky gift to bring it with you. Nobody here could imagine to eat it, but it would be a very originally american prodct according to the Germany opinion I think. ;-) Children do not see any differences between american and european toys, so it doesn't matter what you bring with I think. Greetings from Stuttgart!

Don't laugh, I mean it... I'd be ovejoyed to receive a pack of ziplock bags.

I'd like the Betty-Crocker-Choclate-Chip-Muffins-Mix, I really love them. A friend of mine relly likes Life savers, which I brought her from my last trip to the States.

As another gift for another friend we bought a Starbucks City cup in NYC, which he really liked.