Someone hit sons car from behind at low speed, just a few scratches but it's a new car obviously son wants it done.
Other driver says not to go through insurance and he will pay but should son report it to insurance anyway? If so, how long has he got? He's worried the other bloke might not come through by which time he might be too late.
He doesn't really want to report it if he doesn't have to.
A few scratches?.....these "minor" bodywork dings always involve more work (particularly on a new car that you want brought back to original condition) than the casual look might suggest. It'll probably cost a lot more than you might expect (for an "as new" repair) and the other driver could then refuse payment...how would your son feel about that?
I'd inform the insurance company....which you are normally told to do anyway.