Though popularised by Vladimir Nabokov in the novel Lolita, the term nymphet is actually much older in French, and is notably used by French poet Pierre de Ronsard.
Nabokov did more for pedophilia than the simple coinage of the term nymphet as a whimsical blame for those tender girls of 9 to 14 whom tortured Humbert Humbert so. He coined a whole bevy of terms.
The term faunlet is used to describe the young male counterpart of a nymphet.
“…I met the unblinking dark eyes of two strange and beautiful children, faunlet and nymphet, whom their identical flat dark hair and bloodless cheeks proclaimed siblings if not twins.“
Nabokov also borrowed the term nympholept, a rare, archaic term meaning a person seized by emotional frenzy, as if enchanted by nymphs. The word is found with this meaning in the poetry of Lord Byron:
“The nympholepsy of some fond despair.“
Nabokov used the word to describe one who could “discern” nymphets from other girls. In Humbert’s own words:
“A normal man given a group photograph of school girls or Girl Scouts and asked to point out the comeliest one will not necessarily choose the nymphet among them. You have to be an artist and a madman, a creature of infinite melancholy, with a bubble of hot poison in your loins and a super-voluptuous flame permanently aglow in your subtle spine (oh, how you have to cringe and hide!), in order to discern at once, by ineffable signs – the slightly feline outline of a cheekbone, the slenderness of a downy limb, and other indices which despair and shame and tears of tenderness forbid me to tabulate – the deadly little demon among the wholesome children.“