My kids used to be that one in their toddler years. But when they reached the age of 6 or 7, that's the time when I show them who's the real boss in the house. Most of the times, they knew who it was. But sometimes, they still play the boss in which I ended up as the pawn. The good thing is that, they knew when enough is enough. Just several weeks ago, my eldest wanted to join a school field trip and was nagging us for the whole week. We think is not that necessary and her grades would not be affected by it. This time, we show her who's the boss simply explaining it to her every time she ask for it. But of course, their would be some consequences to it. I'm just waiting for it to come soon.