I bet we all thought that when we were kids, since it's much more visible than the actual urethra! Anyway, it's never too late to learn! =)
The reason why some say that the clitoris is like a mini penis is because the clitoris develops from the same embryonic tissue as the penis.
As an embryo/fetus a male and female both start the same. Basically, at a certain point, if the male hormone kicks in then the fetus develops into a male, otherwise a female. The same embryonic tissue will either become a penis or a clitoris. The same embryonic tissue will either become foreskin or a clitoral hood, etc. It's really quite interesting.
Did you know when a male baby elephant fetus is developing its testosterone levels are high enough that they can be detected in the mother's blood system?!?
...... I watch too much National Geographic...... hehe.