(you know..something specific from the States
You may get them a cute pair of US sneakers for babies ( converse type) because shoes for kids are so expensive in Poland. Actually anything from Gap will do since there is no Gap in Poland yet, so for them it will be much appreciated .
I have a few friends who had babies in Poland and I sent them some adorable little shoes ( for 18 months but it is ok since for newborn there is not much) + pretty outfits ( warm sweaters since in Poland winters are long and horribly cold ... ) They loved everything because i got useful stuff.
Cds can break and toys are great for children when they are toddlers , in my opinion.