Hi HufftheHedgehog:
I'm so sorry to hear your news and I'm sure you're heartbroken for your little boy. No Mum wants school to start off like that.
However, it is early days yet.
My advice is to talk to the teacher but also make a point of finding out what he can play with during recess.
For instance - there may be bikes or scooters especially for P1. If so - is there a bike day or can they use them any time.
Does he like hopscotch? If so is there a hopscotch grid he can play on?
Does he like hitting a ball against a wall? Shooting baskets?
Is there a climbing frame? Are there skipping ropes?
schools usually lay on a ton of these things, but children often don't know to ask for them. School forgot to mention scooters could be used until Easter in Class R to us, so apparently they just sat there brand new and unused in a shed.
Try and find out what he can do at recess, especially on his own and try and show him what's there - may take a few mornings. Usually people want to join play - so if your son starts playing others will join.
Now - I also think play dates (during half-term) can help break the ice.
When is his birthday. Consider a party? It doesn't have to be super fancy or expensive - but get as many round as you can - it really helps make bonds.
Finally - start looking out for after school clubs. This is another great way to make friends.
It is hard starting school - but I suspect he's in with a nice group of kids, they're just all uncertain what to do, still at that age where they play alongside rather than with other children, and probably need a bit of encouragement. Let the teacher know (as we're all saying) it will help nudge them into ensuring nobody is left out, and may benefit more than just your son.
HTH