People on the spectrum shouldn't be given a free pass when they speak about doing something violent, though.
Stating that they are going to shove something down a child's throat is not a joke in any way or form. It is talking about assault. If that is the go-to for this person, there's a serious issue.
No one got hurt yet, but imagine if the employee said this to someone who took offense and responded violently? How about the child that is afraid of the store now? "Oh, we just have to let some people say violent things to us because they don't know any better" just doesn't cut it for me. And I've worked in special education for over 20 years.
First off; many people seem to have run with the idea that because this clerk acted innappropriately, that she must be on the spectrum. As I said in my previous post, it's unlikely given the facts as we know them, but I want to reiterate that even if she is on the spectrum, autism is not a one-size-fits-all explanation to be applied to anyone you meet who is acting "off", and especially not to people who threaten others for no reason. MILLIONS of autistic Americans cannot find or hold jobs in this country because there is a widespread misconception that all autistic individuals are inherently dangerous to others, which they are not. There are a lot of mental illnesses that also can cause aggression toward strangers, and in fact are much more likely to do so than a neurological condition like autism.
I agree that if the owner actually said it was meant as "a joke" then the owner mis-spoke. That's really not unusual; many people who don't know what to call an irrational outburst will try to disarm a situation like this by claiming it was a misguided attempt at humor, because as a society we are conditioned to believe that humor is harmless, while irrationality is dangerous, but the reality is that neither one of those things is always true.
What I do know for sure is that young children take their clues about when to be afraid or angry from the adults around them, and in this case the mom definitely seems to be deliberately keeping the incident top of mind.
Back when I worked IT customer service phone lines, I had an extraordinarily effective colleague who was fond of getting irate customers to calm down by asking them if any babies had died as the result of the problem. Amazingly, that phrase almost always worked for him (though the rest of us were terrified to try it) but the thing is, he wasn't wrong. In the larger scheme of things, a computer problem is normally not a life-threatening emergency, and neither is a muttered threat from a grocery store clerk who didn't do anything else to follow up the supposed threat.
It wasn't a joke, true enough, but the OP *is* over-reacting at this point, and if her child is still frightened, it is probably because he is seeing his parent hold onto her anger about the incident long past the point when she should be. He might even have asked never to go there again partly because he feels that Mom made him more uncomfortable by making a big deal out of the whole thing, or because he didn't like that he had to sit in the car and wait while she had her confrontation with the staff. (I know my kids would have been VERY impatient if made to do that at age 6.)
Kids are not stupid, and after a year in school they have seen enough to know that people often threaten to do things that they have no intention of doing, and that bullies often talk a big game just because it makes them feel tough to talk like that. We teach kids to walk away and not escalate when this happens at school, so what makes the grocery store incident so much different? The balance of power. A customer in a store tends to feel that as the person with money to spend, she has more power than a clerk, and in this case she's making darned sure that everyone at that store (and presumably everyone in her family) knows it.