Of course you all know I feel my intervention is necessary on this one.
Ask yourself, what would scare you more, a 10 year old that knows what the word fuck means, or a 10 year old who has never heard the word once before in his life.
I learned that word when I was in kindergarten (probably before? I don't even remember, I just remember thats the first time I got in trouble for saying it in school), and in all honesty, if you haven't heard it by the age of 10, your parents probably had you locked in the attic every day of your life for the sole purpose of preventing your dainty little mind from being corrupted by the outside world, and they deserve to be shot.