It can be awful. But sometimes it's fun. It depends. A year or two ago, I decided to switch around the cereal, taking the bags and putting them in different boxes. I thought it was a fantastic idea, since it didn't harm anyone, and would be funny. Sadly (or would that be hilariously? I suppose it depends on your point of view), it didn't go over too well - my little brother got so angry when he got the wrong cereal that smoke just about came out of his ears, and when my baby sister got Honey&Rice Puffins instead of Cheerios, she started to cry. xP
So April Fools isn't THAT great, I suppose, but it's kind of fun anyway.
Yes, that is so cute! And I love it when they're little kids, and their parents dress them in sort-of matching clothes where they're not identical, but one kid has a blue dress with white flowers and the other has a white dress with blue flowers. That sort of thing. It's so cute!