I'm jealous of you doing dance classes now though. My knees are gone (at 30!). I'd love to still be in it.
I actually Googled "Adult beginner ballet class" & found two places I was really interested in. I carefully read over the course descriptions and both said that at absolutely NO time is there ever any advanced students or professional dancers allowed in (to make up another class,) to watch, criticise or shame us, or that we'd just feel like ugly duckings next to them dancing.

That description was critically important, as a "beginner" dance class here in NYC could actually mean a "beginner Broadway professional" class made up of people who are professionals & have been dancing since diapers.
This is for adults, a safe environment, and at a level & speed for us in our "adult" bodies, who haven't moved in a while, or may have physical problems - like the bad knees you mentioned. The teacher even mentioned that dance training has changed over the decades. As kinesiology has become a real science, they've found those 50 grand plies (deep knee bends) you & I used to do every class is precisely why we have back & knee problems as adults today.

They don't even make the kids today do that type of training anymore. It's probably also one of the reasons why your kids hip hop is different today (in addition to the change in music.)
You might search around for an
adult beginner hip hop class. It might actually have less knee bending stuff and more of the other stuff that is still a workout and loads of the hip hop fun you remember.
I actually thought the teacher talked too much last night, although he was teaching great technique.
Today, what little we did, I feel it in my calves.

Had he done any more, first class, I think we would lose a lot of classmates returning next week.
I agree, once a week of anything is barely exercise. Why not take them on a bike ride? A family walk?
For myself, once I'm up to speed on my ballet classes & feel more stretched, toned & energised, I'm thinking of trying yoga or pilates. No way would I even think of tackling a yoga pretzel move now.
I think, once a week is a great way to start the kids in dance, and who knows what they will be interested in next because of it. Motion always leads to more motion as the metabolism revs up.

It would be great for PD to take them on tandem bike rides together, later.
