First-timer .... is this "normal" chick behavior?

[JensPeeps]

So I'm a first-time chick owner and this is my very first post ... hopefully I'm doing this correctly! I have 4 baby chicks about 3 weeks old. I have one Buff Orpington, one Black Copper Maran, one Easter Egger and one Speckled Sussex all together in the same "brooder". My question is about their "behavior" ... they are definitely getting much more active and I've noticed that they have begun to "fly" at each other and bump chests .... that is the only way I know how to describe it. It seems to be aggressive behavior, but no one is really getting hurt. They just get all rowdy for a minute or two and then they seem to calm down. Is this normal? Are they just establishing the pecking order or does this mean I have some roos mixed in (all four are supposed to be pullets)?

 

[missnu01]

They are just playing...like puppies do...and possibly asserting some pecking order, but the pecking order is usually accomplished with swift pecks to the head...Lol.