Here's a suggestion to make them stop this incredibly rude and hurtful behavior: tell them in advance. Tell them that the next time they do that in public, you're going to explain - loudly - to their victims that your children just act like BABIES, no matter how much you try to get them to act like big kids. And then do exactly that. A little mutual humiliation is a great teacher. Because what your little ones are doing is mean, bullying behavior. Not just embarassing for you. Also, they need to apologize to their victims on the spot, specifically. "I'm sorry I called you old. You're not old."
Here's a suggestion to make them stop this incredibly rude and hurtful behavior: tell them in advance. Tell them that the next time they do that in public, you're going to explain - loudly - to their victims that your children just act like BABIES, no matter how much you try to get them to act like big kids. And then do exactly that. A little mutual humiliation is a great teacher. Because what your little ones are doing is mean, bullying behavior. Not just embarassing for you. Also, they need to apologize to their victims on the spot, specifically. "I'm sorry I called you old. You're not old."
'Scuse me, darlin'? FIFTY isn't SUPER OLD?? When you hit 50, you're gonna realize just how not old it is!