I don't really know. I have heard of situations where cops automatically assume if a person is combatitve, that they are behaving agressively where if they had the knowledge they have AS, they would know they were reacting in terror. I don't think this might apply to your son yet because he's so young.
I hate to bring this up, but there have been stories of cops tasing neurodiverse people, because they react to being assaulted on by the police in a way that might be seen as violence. If there was a bracelet saying they were on the spectrum that they had to look for, or something else that would tell them from a distance they're dealing with someone neurodiverse. There might be less incidents of cops acting agressively towards people who have a over-sensitive flight or fight response.
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"Sprinkle, sprinkle, little bar, what I wonder is a cat" - Cheese from Foster's Home for Imaginary Friends