Wow, that's a lot to celebrate all in one day!
Optical Illusions are very popular with the older students. Here is a fun link to try some out on the computer: Optical Illusions
ABCYA.com always puts up some activities for a holiday and Valentine's Day is no exception.
The younger students enjoy STARFALL.com. They have several special things to do for Valentine's Day and one the 100th day of school.