They should be on chick starter crumb for 10 weeks ideally. You could introduce some fresh cut up grass when they are 3-4 weeks old but only a tiny bit each day in case they get diarrhoea. Head Lettuce is not good really it contains 99% water and has no nutrients really. Kale would be a better alternative chopped into small pieces, proper "leafy greens" have calcium and vitamins.
Once they are 5-6 weeks old they can start to have a few scraps and leftovers, I feed chick crumb and a little crumbled brown bread, cooked pasta/rice, and oats in the afternoon. Don't give them maize, maize can cause them to lay down fat around their internal organs and can lead to problems laying.
I do enjoy watching them "tear up" a sunflower that can be quite an amazing show! If you really need o supplement tll morning give them milk and crumbled bread for the evening. Just remember to make sure it is good for you to eat then it is good for them to eat.
