Chicks mixed together all day and it was so much fun to watch them all interacting. The 2 big speckled sussex actually seemed to mother the younger chicks, letting them take tidbits from their beaks without objection. Still putting the littler chicks in a separate brooder at night though and it's a good thing. When I went out to close things down, the big kids had taken over the little kids brooder plate and the little kids were not happy. I was surprised the big kids could even fit under the low plate.