Just keep a close eye...I totally get wanting to put him with momma since he is a lonely only...but you are seeing what I saw...the little hangs back and doesn't partake in the scratching...and unfortunately often is getting cold. They get warmed up when she sits and at night, but it can stress them during the day especially if temps are cooler. If he begins to look really rumpled you may have to take him back to the brooder and find a friend for him...I see the rumpled look first, and if that doesn't go away in a day or two, with them beginning to take part with the others, then I see losses.
LofMc
I knew you were probably right but I was hoping. The coop situation was difficult. The ramp had come loose and I had blocked the doorway so babies would not fall out. But I guess mom wanted out and Spot followed. I could not get to them without help or taking the coop apart and I had somewhere to be. Mom was a little frantic about one baby on the ground and the others inside. So I pushed the rest out the door so they would be together and shoved the food under until I could get back home. It's about 80 degrees right now at 3:00. But when I got home an hour ago Spot was dead. Seems odd he was so lively and a few hours later dead. So I took the run apart so I was able to get into it and fix it so they can, if they decide to, go In and out of the coop. I worry that Anastasia will decide to go up the ramp and all the chicks won't follow. But they have food and water in the run and I'm sure she can keep them warm if they all stay together.