My G, who is 4yo.... just started a new "thing" with siblings. He will chase them and hug them until he's tackling them to the ground. he's such a brute,too! He can tackle my 5yo down and then they both just giggle and giggle.
If my other kids are sitting on the floor, playing a game, reading,etc. they are fair game too. They usually play along with him,and they are all giggling like crazy,and G just loves it!
In the past year, he just played on his own, and didn't really pay attention to other people in the room..... so I think in a way it's a positive sign that he's trying to "interact" ,but yet he doesn't know his own strength. I am concerned he may start doing this at school,too. I hope not, or the teacher is going to have a real challenge on her hands!