I am sure that I didn't always get along with my sister growing up, but some days it seems my kids are fighting constantly. I don't know if it is unfair of me to expect the 13 y.o. to act more mature than her 5 y.o. brother or not. My husband says it is the least common denominator theory; all kids act the age of the youngest child. I have to say it has some truth to it. I need to pay more attention and make a note if there is ever a day when no one fights, because I can't remember the last time that happened.