Mice eating babies

[hungba]

Recently, I bought a bunch of mice from someone who was breeding them but no longer wanted to.

I fed off all the males except two, and I set up two colonies. There were two females which were already pregnant and I put them in a separate box.

Those two pregnant ones gave birth to litters of 6 each and they are all raised up fine. One of the colonies, none of the mice got pregnant. The other colony, pretty much all the females got pregnant.

A few days ago, a clutch was laid from that second colony. There were 7 and one died. The other 6 are fine.
Then, a couple days after that, I notice that there was one extra one (total 7) pinkies, so someone laid a litter. But there were some blood and pinky parts in there so someone ate some pinkies.

The advice I was given was that the box maybe too small, and I got a box double the size and put them in it. So at first there were 6 pinkies, then there were 7. Today, there were 9??? I don't know how to react?

Something's not right here, unless someone just laid 2. This time there were two more suddenly, but no blood no parts no sign of eating. I tried watching for a few hours and no one tried to eat the pinkies during that time. I also watched after I changed the substrate once and they were picking up the pinkies and putting them somewhere else but didn't bite them or anything. Funny that they would not put them in the same place, but put them here, one there one elsewhere etc. But in the morning all the pinks are in one corner being nursed.

I was then told maybe its the diet. I use generic rodent blocks that they sell to labs, mixed with some mazuri mice and rat blocks. The box with the 2 pregnant females that did not eat the babies eat the exact same thing and no one ate the babies?

I was then told there may be a problem mouse that likes to eat babies, but no one ate any in the first litter, and with hours of observing I didn't see anyone try to eat them? I can't watch them 24 hours a day...

As for tub size, I already switched them into a bigger tub (HUGE, double the size of before) before the two extra ones appeared... So I wonder what's going on?