I would have done what you did and I do take your view. My DS is 22 months and is exactly the same. He loves to play with the big kids, often gets knocked over, thinks its hilarious and generally has a ball.

I let my son go. To date he's always been fine. He loves it and I love watching him happy.

And if he gets hurt? Well, I'll dust him off / take him to hospital if needed and all will be fine then too.

My DH is a little like yours although not to that extent. I just say to him that if you are uncomfortable with what is going on then you do something about it but I'm not worried. When he hears that I'm not worried he generally backs off.

It's a hard one and I think it will get better with time as your little one gets bigger.