✔ 最佳答案
There is no particular age, but before that child hits puberty, they will be uncomfortable with it themselves, and push their parents to let them go alone.
In the meantime, more and more stores and sports arenas have family bathrooms which are designated this way specifically so that parents can take their opposite sex child with them. Also with the transgender bathroom rights movement, some businesses are moving to all the bathrooms being unisex, so that's another reason why parents will not be criticized for bringing their children into the bathroom that the parent uses.
I see it as a good thing that the dads you saw were at a sporting event with their daughters, and going to the bathroom was just a necessary part of that.