I also just started a 1.3 colony, all 3 of my females were noticeably pregnant, and then the other day one of them was really skinny but I couldn't find any babies or evidence of any either. I assumed they ate them since a lot of first time mouse mommy's do. The next day I checked on them again and one of my other mice had just given birth to 7 babies! I was so excited and hoped they wouldn't get eaten. A few hours later, I heard some loud chirping coming from the tub, so I ran over to look and the last female that hadn't had babies had taken three of the babies out of the nest box and was killing them. Needless to say, I've removed her from the main colony, and as soon as she has her babies she will be snake food lol. I cleaned the colony's tub out when the babies were just 2 days old, and they didn't seem to mind at all. I just stuck the babies back under the nest box when I put them all back in and they built the nest up around them like nothing happened. It's pretty cool because I have a clear tub, and if I slide it halfway off the table, I can see the babies and momma from underneath. They have no clue I'm watching them so I get to see them interacting normally. Such little cuties!