I have two 1 week Buff Orpington chicks and two 3 week old chicks, Buff Orpington and Danish Brown Leghorn, that I am wondering when I should let mingle together? Right now I have them in the same brooder, but separated by chicken wire divider. The 1 week chicks are closer to the heat lamp and separated from the older chicks. Are they close enough in age that I can remove the divider or should I wait until they are a little bigger?