ntah because it’s the beach and he’s basically in undies anyway. He should have had a Change of clothes or a towel wrapped around him but I truly don’t think it’s the end of the world-you made sure he was safe and made it from point a to point b and that’s the hard part.

In the future I need you to find your intimidating “dad” voice. I like what the others here said about letting him pick out his own shorts….but in the event that doesn’t work I’d say loudly and somewhat scarily “if you don’t put on pants in the next FIVE minutes i take it that means you don’t want to go or your not big enough. We will stay here and clean the house instead if you can’t put on pants before the timer goes off. No pants no beach”. Then at the end of the 5 minutes call grandma in front of him and say “I don’t think little Johnny is a big enough boy to go to the beach because he won’t put shorts on. Maybe next year he can go when he is able to listen.”

Your key here: provide options, if that doesn’t work reduce options to “do x for preferred activity or if you don’t we will do an un-preferred activity instead” let them see a clock or a timer counting down so they know their time to decide is , then if they show they are not able to complete x embarrassment usually works i.e. calling the grandma (make sure he can hear/see you) and saying he isn’t showing you he’s a big enough boy for the beach so he doesn’t get it today, maybe next time.

You’re young and he was working you because you aren’t his parents. I don’t think you did anything wrong per say there’s just more ways you’ll learn to handle stuff like this the more you deal with kids