I usually begin "scratch training" when they are around 7-8 weeks old, shake the jar, then sprinkle a tiny bit on the ground so they begin to associate the sound with goodies and later will come home from free ranging to that sound. I rarely give them anything except starter, eggs and yogurt until they are 8-10 weeks old. I never have any leftovers to give my flock--we eat those, no waste here. If they get anything else, I have to buy it for them. And I may buy a bunch of kale or dark green leaf lettuce on occasion for everyone, but mostly, they get the feed appropriate to their age.
That said, when they are raised by a broody, they eat all sorts of things out and about.
That said, when they are raised by a broody, they eat all sorts of things out and about.