A fifth grader's understanding of human reproduction

"Basically mom, all the little sperm are like soldiers going to battle and the egg is like a cannon shooting out of the fallopian tube." Through much giggling and the making of battle noises (where my son corrects me and says"gather more spit in your throat" when I lamely try to create an explosion sound) my son learns the basics of fertilization one evening at bedtime.  Right now, sex seems to be a mysterious act to him where egg is conquered by one brave and valiant sperm.  I know someday the discussions about sex will be more more intricate and emotional, so for now, the battle of the sperm and egg is a memorable bedtime story.