I can't tell you about Croatia specifically (first trip there will be in April)---but I do have experience traveling with infants as young as 4 months to Europe. If this is your first child, and they will be born in January or Feb, your wife may feel less ambitious for travel once the baby is born. I remember colleagues wondering what they were going to do during maternity leave and thinking they will be bored. Believe me, it will fly by and your wife will feel occupied and busy.! Having said that, we did go to Europe with my 3rd child as a baby. The key is to have simple and direct flight plans. If you are traveling from the US and going to Croatia, consider the flights first. Simple travel plans without a lot of logistics (the number of planes, trains, automobiles) are key. Car travel is more difficult, as car seat is needed. The amount of gear you may need will be a bit overwhelming. We did not bring either a stroller or a crib. We brought with a baby bjorn (which worked very well) and the place we stayed had a crib.