In the 16th century, France celebrated the New Year just like we do today, except they partied on April 1st. In 1562, Pope Gregory changed the calendar to the one we use today and from then on, the New Year began on January 1st. Those who didn't know about the new calendar, or ignored it and kept celebrating on April 1st were called April fools and everyone played tricks on them.
In France today, April 1st is called Poisson d'Avril, which means April Fish. Children tape paper fish to their friends' backs and when the young "fool" finds out, the prankster yells "Poisson d'Avril!" In England, tricks can only be played in the morning. If a trick is played on you, you are a "noodle." In Scotland, you are called an "April gowk," which is another name for a cuckoo bird. In Portugal, April Fools' is celebrated on the Sunday and Monday before Lent. Pranksters usually throw flour at their friends. Nice.
Here's some traditional April Fool's Day jokes
Got Milk? If your milk comes in a cardboard container, add a few drops of food coloring. It's harmless.
For a fruity April Fool's practical joke, get a few gummy worms and carefully poke them into fresh fruit, particularly apples. Mom will love this.
April Showers: Put a rubber band around the kitchen sink spray nozzle handle when nobody's looking. Make sure the nozzle is pointing up and outward. The next person to use the sink will get a splash! Too funny!
Here piggy piggy. Let three pigs loose in a high school hallway. Funny enough, but first, paint the numbers 1, 2, and 4 on them. They'll be caught quickly enough, but imagine the time spent hunting down number 3.
I won't be playing any April Fools jokes this year, mine's in the White House.