Even in normal times, please don't keep mice in cages. If you want them to have babies, please keep them in cages rationally, that is, under your supervision, because you didn't separate the cages before, which led to the subsequent uncertainty. If you used to separate cages, you can clearly see that now you just need to observe who is lying in the nest feeding the baby of the mouse. If you have a good relationship with mice, you can try to pick up the mother mice and look at their bellies.
To sum up, in the future, rats should be kept in separate cages to avoid fighting, otherwise you can't tell who gave birth to the baby and hamster. There are bloody so-called blood lessons, you should pay attention to them.