Masturbation
Masturbation
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Definition
Masturbation is the exploration of one's own genitals.  If something feels good, humans do it.  That's what Mother Nature counted on when she created genitals.  If she made them pleasurable to touch, they would be touched, at first by their owner, and later by a member of the opposite sex, thereby ensuring the continuation of the species.
Babies are sexual beings from before birth.  Baby boys in the uterus have been observed having erections.  After birth, some babies begin exploring their sexuality in the middle of the first year, others not until the year's end.  This interest is as inevitable and healthy a part of a baby's development as fascination with fingers and toes was earlier. 

Trying to stifle such curiosity is as misguided as stifling your baby's interest in her fingers and toes.  Making a baby or child feel "dirty" or "bad" for engaging in such play can be harmful and have a negative effect on future sexuality and self-esteem.  Making self-stimulation taboo can also make it more inviting. 

When your baby gets old enough to understand, you will want to explain that this part of her body is private, and that even though it's okay for her to touch it, it isn't okay for her to touch it in public or let anyone else touch it.
Masturbation in infants
Until toilet training began, your child's genitals were mostly inaccesible because of the diaper.  Switching to training pants or Pull-ups made them much more accessible.  The potty-learning process has also made them a focus of attention, heightening your child's awareness of her body.  For toddlers, explorations of all kinds are normal.  While curiosity generally causes the initial rounds of genital exploration, the toddler notes that touching her genitals feels good, and it is that discovery that brings her hands back there again and again.  This may look like masturbation, but in toddlers, it isn't.  The feeling may be pleasurable, but it is not sexual.

Nagging your child to keep her hands out of her pants will only make the activity seem more alluring.  It will also make her think that the good feelings she's discovered are wicked or forbidden instead of normal and healthy.  The best thing to do at home is ignore the behavior.

Touching in more public settings, however, should be discouraged, not because there is anything wrong with the behavior, but because it's considered inappropriate in public.  There is also the risk that it could trigger dangerous impulses in a pedophile viewing it.    Begin early teaching your toddler the difference between "private" and "public", and that some things are okay to do in private, but not okay in public.  If she forgets this and slips her hand into her pants when you're at WalMart, quietly remind her.  Take her hand, give it a squeeze, and praise her for being "big enough" to save her touching for home.

Some children hold their genitals when having to urinate.  If your toddler's genital handling seems related to potty accidents, routinely ask her if she has to go to the potty when you see her hand wander.

Occasionally, a toddler will spend most of her waking hours fingering her genitals.  Like any other comfort habit that interferes with day-to-day functioning, this behavior could be rooted in fears or anxieties.  Or it may be related to sexual abuse or an infection.  If your toddler seems obsessed with her genitals, discuss it with her doctor.
Masturbation in toddlers