I wouldn't use the world "inappropriate" for sexual assault. But you are both right about my use of the word "monster". In all likelihood he is being abused, or has some kind of mental condition.
I actually don’t consider a six year old pulling down his pants sexual assault like I would a sixteen year old. Was is deemed inappropriate vs. criminal is also based on age. This is from an article written for parents to watch out for sexual abuse.
chool-Age Children (6 to 12 years)
May include both pre-pubescent children and children who have already entered puberty, when hormonal changes are likely to trigger an increase in sexual awareness and interest.
pre-pubeSCent ChIlDren:
Common: Questions about relationships and sexual behavior, menstruation
and pregnancy. Experimentation with same-age children, often during games, kissing, touching, exhibitionism and role-playing. Private self stimulation.
uncommon: Adult-like sexual interactions, discussing specific sexual acts or public self stimulation.
After puberty begInS:
Common: Increased curiosity about sexual materials and information, questions about relationships and sexual behavior, using sexual words and discussing sexual acts, particularly with peers. Increased experimenting including open-mouthed kissing, body- rubbing, fondling. Masturbating in private.
uncommon: Consistent adult-like sexual behavior, including oral/genital contact and intercourse. Masturbating in public.
Adolescence (13 to 16)
Common: Questions about decision making, social relationships, and sexual customs. ************ in private. Experimenting between adolescents of the same age, including open-mouthed kissing, fondling and body rubbing, oral/genital contact. Also, voyeuristic behaviors are common. Intercourse occurs in approximately on third of this age group.
uncommon: Masturbating in public and sexual interest directed toward much younger children.