I had two pregnant females together with one male. The first batch was born 4 days ago. The second batch was born today. And its hard to tell the 4 day old ones apart from the newly born today ones? Weird. I've bred mice many times and usually i see some kind of growth by the fourth day. Am I wrong? Do some baby mice have a slow growth? I know its not the diet i have them on because I know for a fact i give them the right nutrition and fats to be able to produce and nurse the young. Any one have any answers? Please? 
-Kaleigh
-Kaleigh