T.B.
You pretty much can just never leave them alone together until this passes. I would bring my toddler into the shower with me just so I could take a shower, or if the baby was napping in her crib I would close the safety gate on her door so my son couldn't get to her while I was in the shower. I also gave my son so much positive attention at this time. Praising him when he was gentle or helpful or playing independently. Sometimes I would try to get him involved in an activity before I started dinner or whatever it was I needed to get done. When possible, I would have him help or make him busy "washing plastic dishes" at the sink to keep him busy. This activity is really messy, we had him strip down and put lots of towels on the floor but occupies lots of time. Whenever possible we tried for him to have extra one on one time with daddy too. When there was an issue, I disciplined him, but without a lot of emotion or attention, just put him in time out, explained why and made him apologize when he got out. I tried really hard not to scream or yell. For us, it took about 3 months for him to be consistently gentle, but I didn't trust him alone with her until she was walking and I felt like she could hold her own. Good luck.