Two adults + two young kids = two rooms?!
I would contact the hotel directly and askif they would agree to one kid in the parents' bed plus one rollaway. It's always a hassle with 2 kids in Europa and Asia, but when contacted directly some hotels are flexible and try to find a solution. Not all though. Novotelis is one chain that has discovered this weak spot, they offer a sleeper sofa and free acc for 2 children in most of their hotels.