I work in a bank. Somebody a non-customer came in to cash 2 checks?

I expect you have been trained in money laundering and due dligence and yes, on this occasion you made an error, but I don't think it matters because it was his mom's cheque, it was for a small amount and she is not going to make a fuss about it even if it turns out that he was doing something he shouldn't (because moms don't do that sort of thing where their sons are involved). Quite honestly, these money laundering regulations are a pain for some of us to have to live with and the people who seem to be punished are the ordinary, honest little people who want to carry out their daily transactions, rather than the real villains. On this occasion you used your common sense and I think you did what this chap and his mom wanted without any fear of repercussions.