Children simply like to be with their parents. Travel is not the crucial factor here. It’s being together in an intentional way that creates the joy. It’s being together as the end goal and not a byproduct.
Of course, I’m talking about normal families which are a huge majority. I hated family vacations as a child because there was no break from the dysfunction. Thankfully for me, in the USSR husbands and wives were rarely given vacations at the same time.