Go out and dig up the worms or pick the catapillars from the bushes, maggots will do too.
I used to have a book about raising all kinds of young animals, I'll see if I can find it in this mess I used to call my home LOL Everything is moving couple of times a year, due to the rebuildings.
Dog or cat food will do for the time being and egg yolk is good too as I remember.
Nice job you've taken on, but don't be too disappointed if they're not going to make it after all to adulthood. By then you'll get the problem that they're not used to find their own food. You must give them what their mother would've fed sometime, otherwise they won't know it's eatable.
Good luck Doc Duncan.
Like scattered leaves...my words will flow