Here's a simple guideline that I wish more people in our society would follow:
Don't touch other people without their permission.
When I started this post, I was thinking specifically about ways in which some bodies are sometimes treated as public property, such as white people touching black people's hair (and more generally, anyone touching other people's “unusual” hair), and people touching pregnant women's bellies.
But there are obviously lots of other contexts where this applies, too, both minor and major.
There are, of course, exceptions. If you need to touch someone to avert imminent harm (like pulling them out of the way of a speeding car), for example, or if you're a parent or someone in a parental role. But the contexts I'm tallking about—and there are a lot of them—are contexts where the unwanted touch is not in fact for the other person's good.
...And speaking of kids, I would say that even kids deserve a certain degree of body autonomy, where feasible. Parents obviously have to do a lot of things for the kid's own good, but in other contexts, it's nice for kids to have some autonomy. If you're a family friend or relative, for example, and a kid you like declines to hug you, then I recommend letting them make that decision for themselves, even at a pretty young age. I'm always sad when my friends' kids decide not to hug me goodbye—but I think their autonomy is more important than my wanting a hug.
(I guess that last paragraph is essentially the same thing Fred Small said in a concert twenty years ago: “Now, there's nothing nicer than a good hug; nothing worse than a hug that you don't want. [...] I think what we need to do is make sure everyone, regardless of their age or circumstance, is completely in charge of the hugs that they get.”)
Anyway, my main point here is not about kids per se; it's just that body autonomy is, in most contexts, a good thing and a useful paradigm.
(I wrote most of this back in March, but it fell into the category of stuff that, after I've written it, feels like it's too obvious to say. But I decided to finish it and post it anyway.)