Shotacon
Shotacon (ショタコン,ショタ) is a Japanese and anime term for a sexual complex where an adult, usually male, is attracted to an underage boy. Because such characters are usually bishounen (before or after the fact), it is classically associated with yaoi, although straight shota also exists.
Traditionally written or drawn by women and for women, shotacon fanservice or hentai basically includes depictions of characters under high school age, sometimes with a partner who is usually older.