A guy on a bike sped past my son when he was little and nearly clipped him.

The cyclist, rather than diverting around, chose speed to avoid hitting him.

I say he missed by a couple of mm maybe.

I am quite confident if that asshole had have collided I could have lost my boy that day. Be it his life, or his ability to walk, or brain damage, etc. Who can say.

No, that cyclist needs to be found, and arrested for what it is. A hit and run.