I agree with the advice to make time for your first kid. I was struggling with really negative behaviour from my DD1. She was cross, she only seemed to want to have anything to do with me when I was busy with DD2. But now, when DD2 goes down for a sleep, I make sure I do something with DD1, even if she seems happy for me not to. I find her behaviour is sooooooo much nicer when she's received some special attention.