My girls this morning Lily is still looking a little scruffy but she's on the mend. And I'm super duper proud of her because for the first time ever she walked right into my hand! Tldr; NEVER leave small children unsupervised with pets, especially small ones. And if you are going to breed any animal, do your research, and do it responsibly.
Lily and Maple were bred by a "backyard breeder" who, as far as I can tell, didn't put too much into raising the best possible mice. They're both tiny, meaning either they had poor fetal nutrition or came from a large litter that mum couldn't feed adequately, or both. Mice can naturally have more than twenty babies in a litter! This is because as a small prey animal, in the wild no where near that many would survive. Female mice only have ten nipples, so this is the max number of offspring they can nurse at any one time. For optimum health and growth of babies ideal number is more in the 4-6 range. When bred in captivity it is the responsibility of the breeder to ensure that large litters are culled down to this number - either soft culled, where they are "adopted" out to other females who can nurse them, or hard culled, as in euthanised. It is in the best interest of both mother and babies that this happens.
On top of that, both these girls and the third I took in at the same time are super duper hand shy. The third girl, Oreo, died not long after I got them. I am their third owner - that's a lot for these short lived creatures. The person I adopted them from gave them to me because of how shy they were. Before that they belonged to the breeder's son, who clearly terrorised them. Unintentionally, but the damage was done. Apparently the child was under five and grabby. No wonder they are scared of people. I've had them for seven months now, which means they must be approaching a year old, and they've only just begun to trust me. Animals have feelings too. Keep that in mind when you choose to have, or especially to breed them.