DS is 7 and Dd is 5 and sometimes, unless they are reading or on a screen, it seems like they are in an ongoing battle.
I know it's perfectly normal but they NEVER play together.
It just seems sad. I has them close in age so that they would play together.....a cunning plan 
I've tried praising them when they are kind, punishing them when they are little gits to one another.
Any other ideas?
Tia