my dd1 ( 3 1/2)has recently become a nightmare. i found her this morning trying to pull her sisters (11months) head off. she thumps her on the back, and fair enough dd2 can fight back reasonably well, she grabbed a fistful of her sisters hair the other day in retaliation. i told them both off, put dd1 in her room and dd2 in her cot for a little while. but it was the way this morning dd2 was convinced her sisters head would come off if she pulled hard enough. its scary. anyone got any ideas on what i can do?