I waited until mine were 3 wks old and started with grit free choice and a couple meal worms each.
They LOVED them and LOVED me for giving them. That's when they started flying out of the brooder when I opened the top. They'd fly on my hands, arms, lap, back if I was bending over the brooder.
I then made scrambled eggs and chopped/stirred up so the pieces were the same size as meal worms. LOVED that just as much.
I then put in clumps of sod. They didn't know what to do the first day but the next day after work, it was just dirt that was left.
I never did the plain yogert or cooked oatmeal that some do. I tried to stick to things they would get from mom if they were out free. (Although, mom wouldn't have cooked up some eggs. I just thought the balance of protein, fats and carbs was good).