If you start typing letters in the search window in the upper right-hand corner of my browser, Google will helpfully suggest search phrases that begin with those letters for you.
If you type in the letters S and E, for example, one of the options is Sesame Street. Another is sexual intercourse.
If your computer-obsessed (and remarkably computer-literate) preschooler types in both of those letters for whatever reason, guess which option he will pick?
[Time for parental controls. I wouldn't have been so freaked out about it, except the kid can read and I didn't want him repeating that at preschool. Also, he'd clicked on the Google Images tab. I supervise him when he's on the computer, but he was fast.]