My niece has been going to games since it was 3, although we had taken it to FNF long before then, (not a real climatisation, but it worked). The child once went in the Family Stand, and when we met with it and its mother after the game, it said it would never go in there again; I think the child was 6 or 7 at the time. But then again, it is a mad child (no, it does not take after me...).
I don't know if this helps, but you could get yourself a ST in the Kop, and if you wanted to sit in another part of the ground (say to take your kid into the Family Stand), you can change seats for the game; I do know that if you go somewhere that is more expensive, you have to pay the difference. I don't think you get anything back if you sit in a cheaper seat. Hmm....