Yes, they do this for a head count of 6, even if a couple of the heads are small.
We're a family of 6, so we're used to it. The most important thing is to make sure that whoever is settling the bill knows that this charge is already in there, so you don't double-tip. We never argued with the amount, although I've heard that you can if you have lousy service. And of course, you're free to add more if you feel it's warranted.
I think it's a bit high, but everything at WDW is, and it didn't bother me enough to make a fuss. I'm used to it costing us lot when we eat out (so we rarely do it at home).