I am not too sure what you are trying to say. Did you separate the babies from the breeding colony and then put them together? Or are the babies still separated from the breeding colony? Are the breeding colony and the babies from the same colony or are the babies from the same colony, different from the breeding colony?

Here is the thing. A breeding colony will not accept any new members into the group, that includes those who were once part of the colony and were pulled apart. This includes babies, even their own. If the babies were not separated from the colony, the move from the sellers house to your house would cause stress and that would mean complete annihilation of the babies. If the babies were separated from the breeding colony in their own separate tub (which I think you are trying to say) then yes, they can kill each other but this is very doubtful (if we are talking hopper baby size or smaller). Anything younger then 21 days has a high chance of not making it without their mothers, so if you had babies younger then that, most likely they are just dropping like flies, but in this case you would be seeing bodies. But like I said, I am not too sure what you are trying to say except the fact that you are missing babies...

If you have them in a tub, yes, they can escape. Their bodies are extremely flexible and tub lids are also flexible. So if the babies at any time can reach the lid, the could most definitely squeeze through.