My 3.5 year old son constantly hurts his 13 month old sister. She can be sat playing by herself and he will walk over and hit or kick her. Hel walk past her and push her over. I understand toddlers can get frustrated but he hurts her unprovoked. We’ve tried time out, taking toys from him, reward charts for good behaviour but are now at a point where we keep them separated as much as possible. If you’ve experienced this what did you do to help? TIA