I don't really think panto is that similar to drag. For one thing cross-dressing in that context is more about a sort of upside-down world, there are also other examples in the show. (Though IMO the best drag is a bit like this too.) And you don't have to have sexualised jokes, or ones that are inappropriate, or that kids really are aware of.
But mainly, it's a show that's generally not just for adults. It's not in a place that is adults only, with characters named for adult activities, etc. Whereas drag is a show, for adults.
I'd not really expect to see panto dame storytime at a library, but at least the kids might know who it was supposed to be. (It might be like having the Paw Patrol Pups, but less popular. )But drag story time, at best, is a bit like getting any celebrity known to adults who the kids are totally clueless about come to read, it's pointless. And it has potential to be more like "adult film star" story time.