What I figure is that foundations dictate the shape of a house, so we've been strict with our two. We scold them, spank them when appropriate, demand "yes sir"s and no buts. Hubby and I want to get all the really tough groundwork laid by the age of six, on the principle that they can't hate us for what they can't remember LOL!
We also give out copious hugs and kisses, tell them we love them twenty times a day, and keep them well occcupied. It's working so far :)
I hope it works. Good luck and remember, even if one gives you grief it won't last too long.