My daughter's birthday is March 15.  She had her first real "birthday party" after she started school, and it happened to be on March 17. Therefore, we began our traditional St. Patrick's parties. Over the years, we did several different things. I usually cut out Shamrocks from construction paper and hid them all over the yard, along with a green doll that was the "leprechaun". Whoever found the most shamrocks got a prize, and the one who found the leprechaun won a "pot of gold"(black coke bottom with pipecleaner handle filled with butterscotch candy. All the prizes were green----frisbees, etc.  The punch was always green, and the cakes were decorated either St. Patrick theme or green (one year I made a green castle cake). Also, the child who wore the most green items also won a prize.  One year, a mother made her daughter a nice green cape.  One winner had on green pants, green shirt, green socks, green belt--even had a green fake bug in his pocket. Every year after St. Patrick's Day, I would hunt the clearance aisles for napkins and decorations at 1/2 off or more for the next year.  One year, I had a pair of twins attend who had St. Patrick birthdays, and they really enjoyed all the decorations. My daughter is turning 31 this year, and I am still decorating in green and St. Patrick themes.