They’re little humans just like you….they’re testing boundaries, seeing what they can get away with. Some are more stubborn than others…later in life obstinance can be a real gift. As far as discipline…consider that human behavior responds to a combo of the carrot and the stick. Set guidelines and communicate them. Good behavior gets the carrot, bad behavior the stick. Carrots at that age are more freedom, time to play, etc. The stick…not a physical stick but a real consequence. Could be a real meaningful timeout, loss of privileges/toys, pushups/laps if you’re coaching, etc can show that there are consequences to not following the rules of the game. Finally, be consistent with the rules, rewards and consequences with your spouse.