So I separated the dad and mom because they surprised with me with bit too many babies. So i took the mom with the new babies in separate box and left the dad with the previous litter (4fmales and 1 male).

And yesterday heard loud squeaking and found the dad biting to blood one of the female babies. She had like 10 bites all over and all coloured in red.

So i separated the dad from the babies, and the wounded one. This morning the baby is better, not shaking in few anymore and generally seems better.

But why did the dad start biting it (found others had a bite on the leg or tail as well, but barely noticeable). FYI none of them bites me.