The late 3's were tough with our oldest. When our twins turned 6 months she totally had it out for the boy twin and would near constantly try to hurt him. It

The late 3's were tough with our oldest. When our twins turned 6 months she totally had it out for the boy twin and would near constantly try to hurt him. It really didn't matter what we did or threatened. 5 minutes after a timeout, or us taking away something she wanted, she would be back at it again. Oh yes, she didn't like timeouts - she would kick and scream and cry during those timeouts. But it didn't matter. All we could really do was make sure they were physically separated as much as possible. That helped a lot. But the times they got close, she usually took advantage and did something to hurt him. E.g. if he was near her path to the bathroom, she would step on his hand while walking close to him. Ultimately, she just grew out of it around 4 years old. But it was a really stressful and unfun time period. She's 5 now, and the twins are 3. She loves playing with them. Until she doesn't of course, but even still - for the past 1.5 years she doesn't want to do anything without them.