One of the forum members had a useful method for keeping and sorting litters. They kept a litter together and fed communally, but after some period started moving non-eaters to a separate container so that they could be given more attention.

For neonates I'd favour a plain substrate, paper towels, just to keep a better view of everything. But I've only had one baby born, and the other babies I've had have been at least 5 weeks old.