I have three children and the youngest is now 42, but each of them is still my child. The word child has never had definite boundaries and common usage has pushed the upper limit higher in the past couple centuries. The laws that deal with this sort of thing seldom use the word child. This is probably more to do with Legalese preferring Latin root words, so minor wins out over child. Minority, in the eyes of the law is very specifically defined.
I'm just wondering if any of our forum "grammar" nazis will now begin a crusade about how "child" means a certain age range and not any particular minor as if there's a distinction that matters in this context.
That said, calling someone a "minor molester" doesn't have the same punch.