I am a stay-at-home mother of two boys ages 2 and 4. When they are apart, each of them is pleasant, helpful, and easy to have around. But as soon as they are together they are unruly and disobedient. When they do "play" together it's like they're on a mission to destroy everything in sight. I want them to have fun and get along, but they are either fighting or out of control. What can I do?