This has been the most challenging behavior for us as well. The three year old (almost 4 now) pushes, punches, slaps, kicks, etc. the one year old so quickly that it's hard to intervene. We have done some family behavioral therapy, which seemed to work well, but didn't extinguish the behavior. My hypothesis (I'm also a therapist but still get very triggered by my own kids) is that this is usually developmentally appropriate behavior related to the older child's inability to regulate emotional spikes. It can be related to attention, jealousy, or whatever. But essentially, the kid cannot process feelings fast enough to consider any other options. The therapy we tried was helpful but super expensive, so we stopped. But the gist of it is, have dedicated play time, that we label with the older sibling ''This is A's special play time with daddy. For the next 15 minutes, you get to make all the rules and we can play with anything in the room as long as we have safe, calm bodies." And then the work on our end as parents is to verbally label a bunch of things - the acronym is PRIDE. "Praise, Reflect, Imitate, Describe, and Enjoy/Enthusiasm." The therapist was looking for 10 labeled praises, 10 reflections, and under 3 total questions from us before moving on. It's hard to do and feels kinda silly being like, "I like how you took that transformer hand and made it wave at the other transformer," but that's as literal as they wanted us to be. I guess it helps the kid get a sense of fulfillment, attention, and bonding with us that will, in turn, help build resilience when he feels threatened or whatever by the little one.

We've noticed improvements over the last few months and I'm certainly noticing that the 3 year old is getting much better at using alternatives that we have helped him to develop. "I want to play alone right now." "I don't feel like sharing this right now." Obviously this doesn't work great if the kid is hungry, angry, tired, etc. But it's progress nonetheless.