First time posting so I hope I did this right 
My DS1 will be 5 in a couple of weeks and has just started school. He seems to be popular and gets on well with most of the kids.
There is one boy who lives a few doors down from us and we sometimes end up walking to school together along with another neighbour. She has a DD and she is very friendly with my DS (they went to pre school together).
All three are really friendly on the way to school and yesterday played happily when we got to the playground, however this morning we arrived at different times and when the neighbour with the boy arrived her DS tried to interact with my DS but my DS didn't play, he just carried on playing with his other friends. The other boy was upset and cried.
Whilst I don't feel my boy did anything horrible it is worth noting that the other boy comes from a different preschool and doesn't know that many people. I remember being that kid in the playground as I went to many new schools as a kid.
My question is do I steer him towards looking after this boy if he wants to play as that is the kind thing to do or do I need to let them get on with it and ignore the guilt and politics of them being neighbours (and my own experiences of being the new kid)?
I'm really not that confident at this parent thing and could do with some input.
Thanks