My DS is in year 3, on 2nd centile for height and weight. My OH is only 5ft6 which makes it easier as he sees his dad is short and it doesn't bother his dad. He went through a stage at the beginning of year 2 when he kept asking if he would ever be bigger like the other boys in his class, we were just honest with him and said probably not as your dad is small, but you are perfect just the way you are. It doesn't seem to bother him now at all, and he is very popular and happy in school. We also had tests done a few years ago to make sure there was nothing stopping him growing but he is fine, just short!
We may have an issue as his younger brother grows up as his brother is tracking taller than him, and mum dad is just over 6ft so I think his brother will end up being taller than him but we will deal with that when/if it happens.
We just make sure to always tell my son he is perfect they way he is, and everyone is different. I've not had many parents comment on how short he is to me, but it doesn't bother me when they do as he is short!
It is reassuring to hear from others with short boys anyway, as my son is in a small 1 form entry school, and is definitely one of the shortest!
I hadn't heard anything about certain sports encouraging growth, I though it was all genetics but tbh unless my son really wanted to do a particular sport i wouldn't make him, I think he is just the way he is. He is very active anyway but not sporty at all, just likes running around with his brother!
Try not to worry about it too much, I am sure your son is perfect the way he is.