How to Guide Without Crushing...

Personal space would be part of his social interaction aspect in his IEP. It will definitely have to be addressed because as the children get older, it will become more important. When children like ours are teens and they happen to be physically affectionate (my daughter is not, she has an aversion to showing much physical affection due to her sensory processing issues) it can often be mistaken for being too physically aggressive or as sexual harassment.

So much of it is about reading social cues, but in kindergarten I think that ALL of the children are having this particular issue that you're having. The really physically affectionate children who are also bubbly and infectiously excited about being around other children just can't contain themselves while others are more cautious. I sincerely doubt it's about your son having ASD right now, you know? Not as a kindergartner.

What I might do is explain that some people don't hug as much in their families as in other families, or they don't hug their friends as much as they might hug their families. That means that when we're at school it's a good idea to ask friends for permission before giving hugs.

I say this because of the type of child my own autistic daughter is. Hugs are misery for her. I have to ask her for permission, and we've trained family and friends to ask her for permission too. Sometimes she says yes, sometimes she says no. The best is when she offers her own special alternative to a hug.

My son actually had a group as part of his IEP. They practice role playing, appropriate conversations, personal space, stuff like that. It helps for the obvious stuff.

In my son's Kindergarten class, there was a boy like that.
His Aide, helped him, and coached the parent about it.
AND the Teacher, also talked to the entire class about it. About HOW THEY CAN... POLITELY tell the boy "thank you, but that's all now..." and move away. But all the kids, were very kind to this boy. They really liked him. At no time was he treated as a misfit.

I also work at my kids' school, and there is a high functioning Autistic boy there, who is also like that. He LOVES to hug me, and tickle me. As a school staff... I cannot encourage things like that. Bodily contact etc. because it can be misconstrued. So I tell him "thank you, but hands to ourselves...I'm not your Mommy. " and he understands. I also told his Aide as a head's up. His Aide knows how huggy the boy can be. But the thing is, he has improved from before and he does not take it personally. He still smiles and I praise him about his "good manners..." and "respecting other's space..." etc. He understands. Or, he will ask first "can I hug you?" (I have taught him that to ask first, is having manners..) and I will say "Okay, but only for one second... " and he does so. Or I will say "not right now..."
But overall the boy is fine.

You will not "crush" your dear son's personality. He is just learning, socialization. And you teach a child, that everyone needs space... and everyone is different. I even taught my kids that from when they were Toddlers.

Whether or not a child is on the Autism spectrum or just a "regular" kid... they can be huggy. Some kids are just like that. But so we navigate them. You will not "crush" their spirit.

Lots of the kids, in my son's class (he is in 1st grade)... are VERY huggy and affectionate. Boys and girls. Being I am in the class and at school, they all do this to me all the time. So I will count "One, two, three....okay thank you!" and then pace myself away. Bear in mind, not all parents "like" if their child is hugging/holding/being cuddly, with other "adults" or children, either. So I am aware of this.
And also, our school Administrator, "coaches" us too, on how to handle things like this.

Its just a hug. Sure. And its a natural inclination for many kids.
But well, everyone may not like to be hugged.
It is just learning "manners."
And tell your son there is no need to take it personally, not all people like to hug. Which is true.

Use social stories. There are lots on the net regarding personal space. He is one: http://livingwellwithautism.com/social_stories-behaviors

I have one of those boys that would *totally* shrug out of his embrace...b/c he can NOT stand to be touched, ESPECIALLY by strangers. He has a very firm idea of his personal space and I have had to talk to him much the same as you will have to talk to your son.

I told mine that their are those who love to hug and to touch just as much as he hates it...and that he should always be polite, but that there is nothing wrong with exiting an uncomfortable touch!

So maybe you can just talk to your son about kids like mine? As much as he likes to touch there are those that hate it equally as much!

If you say it in a nice way you won't be crushing his spirit...just teaching him about others' likes and dislikes.