SEND? Social anxiety? please help....

[coffeealldayandnight]

I have a little boy who is starting school in September. He has always been incredibly introverted, preferring his own company and the company of his closest family members in his house. This, of course, is fine and it is great he feels safe to be confident and happy in his 'comfortable' place. However, he struggles enormously with activities involving anyone else and communicating in difficult circumstances (if his sister takes a toy or he doesn't want to do something) where his behaviour becomes difficult and disregulated including arm flapping, loud crying, howling. He goes to a pre school for 5 half days and everyday it is a struggle to get him out the house and through the door, once there, he says it is too loud and would rather sit in the book corner or talk to the teacher. However, the worst situations for him, by far, are play dates or social activities like the playground/soft play/parties where he runs in circles howling and flapping him arms, often showing such disregulation that he ends up hurting his sister through frustration/lack of understanding of his emotions, or lying on the floor screaming. I just want to help him, i want him to know that other children aren't scary or a threat and how to communicate when they speak to him or want to play (he often turns his back and runs off) and even just a way to help him become calmer when he finds his sister tricky! I avoid lots of social situations as much as possible but he has a sibling who loves the playground and meeting friends - as do I and it's getting me down that I'm unable to attend play dates, coffees, weekends away with friends or parties (I know that sounds so selfish). We are becoming more and more reclusive as he is getting older which I'm sure isn't right? He often does a very loud yowling sound when he is out of his comfort zone which can be in the middle of a shop or even at home if he isn't sure how to communicate his needs (despite being completely able verbally). With us, he appears completely neurotypical, in terms of good chat, knowing his numbers, enjoying puzzles and outdoor play, he is funny and sweet, kind and curious about the world. Does anyone have any helpful hints? Does it sound like I need some extra help for some SEND? Or is this just a typical developmental stage? If so, what help?

thank you

Kindly, it sounds like you are doing an amazing job of meeting his needs at home, by keeping everything safe and predictable and he is able to thrive. However once he is in an environment that is not as predictable and well managed he is really struggling, beyond what might be seen as just a developmental delay.
It is a tricky time for getting help and support and onto an assessment and diagnosis pathway. If preschool haven't already flagged that there is an issue and suggested an assessment pathway, then school are unlikely to get things moving in his first few weeks - they will want to give him chance to settle in.
I would advise that you find out whether there is a 'health' route to an autism assessment pathway in your area so that you can go via your GP as a parent referral rather than waiting for school (some places only accept referrals from education). Not diagnosing over the internet, but it seems like the obvious starting point.
None of this changes who he is, and with or without diagnosis he will continue to be the chatty, engaged and curious boy that you love.

@Bubbleswithsqueak thank you for your lovely reply. I think that sounds like good advice. I will make an appointment with the GP as soon as possible to get the ball rolling with an initial ASD assessment.