The earliest mine will eat is 3 days after their first shed--most will eat 5 days after. A few hold out longer.

I offer live rat pinks or fuzzies first. Several of the animals usually take them. The ones that don't, get a mouse hopper--the rest of them usually take the hopper. I alternate the offerings until all the babies have eaten. It never fails that I'll get at least one that has to be assist-fed to start at all, but so far I have gotten them all to eventually start feeding on their own.

If a baby seems reluctant, I have also found that offering a mouse crawler works well. It is less mobile and less intimidating, and can be left in safely for longer. Don't underestimate a hopper's teeth. They can eat lab block.

Interestingly, there are some babies that do not want mouse hoppers--they prefer rats from the start.