But many upper middle class people have nannies, au-pairs, etc. Upper middle class isn't very large, but they are certainly the demo for an AirBnB in a tourist destination. Average people don't really travel much.
Even if you don't have a babysitter, having a kitchen to feed your kids yourself is huge.
Maybe in the US, here in Europe I feel it's absurdly common for even the low middle class to travel around.
Similarly, many US households have access to a car. Most American vacations are road trips.
Getting a 3 bedroom vacation rental instead of a 2 bedroom and driving the au pair up in the back seat is not solely the province of the super-rich.
[For the record: I do not have an au pair, nor have I taken a babysitter on a trip.]
It's a job, sometimes you do in the family sometimes you outsource. No need to be super-rich for it.
I'm pretty sure you already know that travelling with personal domestic staff is a vanishingly tiny niche requirement of the super-rich.