I usually wait until about a week after the first shed. If the babies are set upi right (individually in shoeboxes, hides, and good temps), about half normally eat at this first opportunity. Feed them all again about 5-7 days later (dont try to feed the non eaters in the mean time...just try again the next time). Don't even consider assist feeding unless they haven't eaten after about a month post shed.
As far as the food item to offer, you'll here conflicting advice. I swear by my method, but other suggest otherwise. I know what I do works, and I've never had any problems. I feed very large fuzzy mice (what I call crawlers - eyes open, starting to move around) for a first meal...DARK in color. Doesn't matter if they are brown, black, whatever...but they seem to prefer dark over white mice.
Also, although some will take mouse hoppers, for a first meal I avoid these. The hoppers are a bit spastic, and tend to freak out the new babies.
Good luck!
Joe Pociask Pythons