The screaming brat problem is different. The fat pas problem is actually solved by providing an extra seat for which the pas must pay. The screaming child problem wouldn't be solved because just the fact that they have to pay doesn't stop them from screaming.
So one is a solution to a problem and the other would be a fine for screaming kids, which is not ok, as much as I loathe screaming kids.
But it would be nice if FA had an abundant supply of ear plugs on hand. Perhaps they do. I always bring my own.
Till