Mmmmm, I've got one of these too! Not quite as bad as your daughter but wears me out some days, drives his dad up the wall, we've got a real battle of wills going on there ;)
I have thought about the reward stickers myself, might just give it a go. Agree that NO has to mean NO, DS is getting sent to his bedroom more and more often....(naughty corner no good).
I remember my ds1 being a bit of a tyrant too, was worse in some ways, but I think we have been a bit more laid back with this one, god in some respects but not in others. I do think it's a phase though, to a certain extent -the I'm the Lord and Master of the Universe complex they seem to get at this age!- and my older son has nearly completely got over it, (he's nearly five) but they do need reminding who is boss, and it defintitely isn't junior or juniorette!!
