It’s a pretty common but false rumor on here but chicken feed or chick feed does not have grit in it. Even if crumble or pellet form it’s already been ground up so they don’t need grit to regrind it. It’s such a common myth that I e-mailed Purina about it. Nope, their chick feed does not contain grit. So don’t count on them getting grit from chick feed. They won’t.
If they eat much of anything other than chicken feed they need grit to grind it up in their gizzard. Romaine lettuce certainly is included in that, if you are feeding lettuce they need grit. Bananas and yogurt, not really. I think it is good practice to provide chicks grit at a really young age anyway. That way I don’t have to worry about it.
Chickens of any age can be reluctant to try anything new. I regularly toss stuff from my garden into the run. The adults might eat it immediately, they may ignore it for a while and eventually eat it, or they may forever ignore it. I can get the same different reactions with the same stuff, cabbage leaves for example. The chicks can be as bad or worse.
About the first thing my broody hens do with their chicks is to take them to a patch of dirt so the chicks can start pecking. They are getting grit. She will get them to eat certain foods after that, so they certainly can possibly eat green stuff from an extremely early age. But most of my broodies don’t immediately take them to grass to eat, they peck a lot at the ground at first, probably getting dried bits of food from that.
My suggestion, after giving them grit, is to just make the treat available. Chop stuff like lettuce into pretty small bits. Then be patient. Eventually one will get brave enough to try it and the others will then join in. Or they won’t. It’s not a life or death decision, they don’t need anything other than chick feed. It contains everything they need. The general recommendation is to not feed many treats at any age so they continue to get a balanced diet by mainly eating their feed.
