If you have more than one child, chances are you have experienced sibling rivalry. They could be fighting over a toy, who got to the car first, or because one of them breathed on the other. Ariella Lew is a former paediatric nurse and the founder of Kids on Track, an organisation dedicated to helping parents understand and care for their children. Ariella explains what's going on when your children fight, and the best way to respond to their squabbling.