Yea its definitely okay for them to be outside. You need to worry about your whole flock getting too hot tho. For the babies you just need to put them in a smaller wire cage inside of the big girl pen to get them used to each other. For the bigger pen, think about moving it to under a tree or a...
I usually get rid of older hens every time I breed a new generation of cuckoo sizzles, so if you are willing to travel towards me the next time I breed I should have some hens.