Having visited with little ones - typically one parent joins the line with the rest of the kids while the other parent heads off to the restroom and may want to join their family. That way they avoid inconveniencing people twice, by going out of the line, then back joining their family. I know, I know, "Just have the whole family join the line when they're done!" Whatever. In general, I find this to be such a rare experience and with so little impact on my actual wait to get on the ride (or wherever) that I choose not to worry about it.