> It's Dorchester, the kid could have found it on the way to the bus stop.

Statistically, way less likely than finding it laying around their own house.

I do think it's more plausible than the Lock Picking Lawyer safe-breaking wunderkind ideas being discussed above though.

I mean, I'm sure most responsible people toss their guns in the Charles after they're done with them for exactly this reason, so a kid doesn't pick one up on their way to school, but you can't count on everyone to be responsible.