At 3 months of age, I'd still feed a chick starter or an all flock feed. Laying mash is generally low in protein and has too much Calcium for growing birds.
I will I use rhe medicated chick starter whwn I first get them from any
tractor supply place . First round a few years ago I lost 6 over night....when I realized what qwnt wrong I wanted to go round up all the babies from these places and nurse them...I had a heat lamp ...but I put a heating pad wrapped for their protection to see if they would gravitate to the extra heat..plus put a little sugar in their water. ( hypothermia alot of pet owners don't understand that low blood sugar can cause this an Sudden death) I ate and slept with them. I didn't leave them unless I had to . I treated them like I would have if it was my hand reared love birds o use to have. I didn't realize these places don't really do what is supposed to be done or hire people and not train them to care for these fragile babies. . Ibwrote down what you told me so I have it on hand fie now an future use. I wish I could get my hands on some prozyme that uses to be sold for animals . I had to order mine years back. It was some great stuff. If crops were stopped up a little bit in drinking water woukd help break the food down to liquid. I sprinkled a little from the tiny scoop over my dogs cup of food ..as suggested an just dampened the food. I got busy about an hour later I went to get her food ..it looked spongey. I stirred it and it had completely turned to liquid. It mad raising those babies easy. ..I had gotten them from a lady who no longer wanted them. 1 set woukd hatch babies then not feed them. The other set would kick them out of the nest as soon as they got pin feathers..I learned in correct humidity (to low) would cause their food in their crop to dry out.. the 1 that would not feed her babies was sweetie..the 1 that woukd kick then out as soon as they got pin feathers was mean and named B for biotch. I am rambling I am sorry. ..I just love animals ..this chicken I have inside is pacing wanting held. As soon as i open rhe cage baby come s to me and lays on me. ..