"Fetish Fuel" could be a sub-trope of common fetishes, one category could be Hot Parent (not Hot Dad, not Hot Mom, but Hot Parent, merge the two as a "Parent" trope, same thing with "Bumbling Parent", there is a "Bumbling Dad", but no "Bumbling Mom"). However, there are Bumbling Moms on TV, in movies, etc.
There could be divided categories, such as "Hot Dad"/"Hot Mom" (on the "Hot Parent" trope article), and "Bumbling Dad"/"Bumbling Mom" (on the "Bumbling Parent" trope).
Grandma/Pa, What Hotness You Have; Mr/Mrs. Robinson; could be categorized this way. Don't know if there is a spear counterpart for Stacey's Mom.
Fetish Fuel, as I said, could be divided into categories, it could apply to "Hot Moms", but it is also applicable to "Hot Dads."