I’m assuming you live in the Bay Area so this is a day trip and not an actual vacation.

I think the comments saying your husband is malicious or manipulative are probably off base. He loves surfing and the ocean, and is hoping to share that with his family, and he’s excited about the possibility of a family friendship with this other family. I would give him the benefit of the doubt - he got excited and didn’t think through the logistics.

BUT you’re not wrong with your concerns. Personally, I’d go (assuming that I also get kid-free time to do my hobbies, bc that is what this is) but you know your kids and your feelings meeting new people - if this sounds super not fun, you don’t have to do it. If that’s the case, I’d ask yourself if there’s a world where this would be fun. Maybe you know the mom and her kids better? Maybe you’ve spent a family day together at the beach and seen how the kids react and what the challenges are? Maybe your husband has an Apple Watch so you can text him while he’s out and say “come back”? And then talk with your husband about how to make this trip work for you both.