Kicking, hitting and screaming. It's what happens at my house from the moment my kids wake up to the moment they go to sleep. My sons, ages 2 and 4, fight with each other over everything. Whether it's sharing toys, the color of their dinner plates or even who has the bigger sippy cup -- everything is a competition, and my husband and I are the referees. The fighting is constant, and I wonder every day if it's normal. I grew up with a brother 18 months younger than me, and we bickered. But my parents and I don't remember it being as volatile as what I'm experiencing with my two kids (although I realize we adults tend to block out some of the bad times). My mom friends say their children throw tantrums, but no one seems to relate to my situation. I did some digging, and it turns out I'm not crazy. Sibling rivalry, especially when it comes to kids of the same sex, is common -- and even more so when they are less than two years apart, according to Nationwide Chil...