Don’t add them in with grown up chickens, that will definitely make them not happy.
Keep them warm.
For the first week you have to keep them at 100 degrees on one side of their box. The other side of their box is the cool zone. They eat in the cool zone and sleep in the warm zone. It’s important to make sure the whole box is not one temperature, they need to be able to get away from the heat on one side of the box.
Then you drop the temp 5 degrees each week. So on the 2nd week it is 95 degrees on the warm side.
I use this temp controller to keep the babies nice and toasty warm but not too hot, so they keep growing healthy.
Keep them fed.
I feed my baby chickens standard non medicated chick starter. I take the lid off the coffee can and use it as a food bowl.
And I use the lid of the spice jar as a water bowl. Because if you put too much water in there they spill it and get water everywhere and make a big mess.
I put the little water bowl on the food bowl so even if they spill the water and the food gets wet, they’ll still eat the food.
Using the little food and water bowls means you’ll have to attend to the baby chicks at lest twice a day.
Just leave them alone and let them grow, you don’t have to do anything.
Stress makes chickens sick and brings them down. You need to keep them in a quite area. They can take handling and holding, but then you put them back in their quite area. No animal likes noise and stress. So don’t keep them in the kids playroom.
People do too much stuff, leave them alone and let them grow.
Use the tub they grew up in as the nest box when the time comes, it’s such a good re-use. The link to the how to make a nest box video is here.
Get the temperature controller and bulb here.