3 week old RIR (I think). Please tell me NOT a roo

[Jaks1512]

That is too much of an age gap unless your older birds are very docile. If you put them in together the older birds could possibly peck the younger ones to death.

I planned to introduce them using the playpen method when they are around 6 weeks old. I am just not sure that will work the same way with only one chick if the other ends up being a roo