Masubi, you are right that children masturbate. Even babies masturbate. It's been proven that they'll go after themselves while in the womb. Let's face it, if something grew on you you'd want to check it out.
Masturbation is a normal part of life and sexual self expression. Only you know what feels good, and masturbation helps you figure out what you are and what you are not comfortable with. This allows you to better say "yes" or "no" to your partner because it gives you the confidence to say what you feel. It's your body, and you should be comfortable with it.
If you look at the evolution of the human race, human sexuality makes a good deal of sense. According to several census reports, there are more women in the world than there are men. In fact, women are more likely to have female babies than male babies, a 3 to 1 chance last time I checked. Part of the reason that this is true is because of how women would sometimes die in child birth or die shortly afterward due to complications. In order for our horny cave man to keep producing, he had to club himself another mate.
Human sexuality is defined by the pituitary gland, a small part in the brain. The pituitary gland is designed for our primitive instincts to take over. These instincts can be defined as the "four F's." These four F's are as follows: Feeding, fighting, fleeing, and... well... let's just call it "fraternizing." (Okay, ********. For those of you who can't take a hint.) The pituitary gland lets us know when we're hungry, when we need to defend our territory and ourselves or loved ones, running away before our butt cheeks get bit off or something worse, and getting it on with a mate or ourselves when the mood won't go away.
I think one of the big taboos come from the church. The United States is a country founded on Christian values, and though we might try to keep open minded, it has ingrained itself into our culture. The church is against masturbation and birth control because Christians feel that every sexual encounter is an opportunity at life. The church feels that sex is a gift from God and should be respected, and the church has had a tendency to beat it into people's heads. Monty Python's Life of Brian can attest to this:
http://www.youtube.com/watch?v=U0kJHQpvgB8 As for myself, yes I do. My husband does too. Sometimes we like to do it alone and other times we get ourselves excited by doing it together. Doing it together is a great way to show your partner what you like and what you don't like.
Be comfortable.
IEditYourWorld