I become one of two things with moms when they're dealing with a kid like that. They either love me or hate me, because I'll walk up and say "Hey, quit acting so bad for your mom." and then chat the kid up with nonsense stuff until they smile. When I step in 100% of the time is if a kid hits their mom... "That is NOT okay." Kids never listen so well as when a complete stranger walks up and reprimands them. 90% of the time, strangers won't even speak to them, and it ends up really easy for a kid to not realize that they are impacting anyone but their mom.