My daughter who is 26 months has started being really horrible to her brother who is 6 months. She scratched him today and drew blood, and often tries to hit him. Obviously am very protective of the baby who gets really upset when this happens. I try not to leave them alone together, but she is more likely to do it when i am around. Have tried naughty step, giving her a firm telling off and ignoring bad behaviour, but it still continues. She also bit my friends daughter yesterday. Any advice?