Wired cages aren't recommended for new babies at all. Until their eyes open and they get some motor control, they can just blindly wriggle between bars and get stuck. I've also read that they can get bad bruising if they're piled against the wires, from the wire putting too much pressure in one spot. Aquariums or cages with very deep pans [3" or more] with no levels are the best things to keep newborns and until they're about 2 weeks.
For full grown babies [4weeks+], a hamster cage isn't nearly appropriate. There's not any room for them to run, jump, play, etc.. Babies need just as much room as an adult simply because they're so high energy. In addition to that, rats grow very fast. By the time most people get them home as young babies, they'll need to upgrade from that very small hamster cage within a matter of weeks.
Hamster cages are very good as travel carriers, but that's about it.