I know I am much harder on my eldest son (almost 7). I have a younger son and the youngest of the family - a girl aged 3.
I shout more at the oldest, demand more and higher standards - I am not as accepting of who he is. Some of this is because he can be a difficult character, but then so can the other two.
I've come to realise I really really do shout and pick on him a lot more and fear for my relationship with him. Does anyone else find this?