We celebrated with a preschool-wide picnic lunch, in the gym due to rain. They were (almost) too excited to eat, and couldn't wait to start running around with their friends and hugging their teachers.
And afterwards, one of their preschool friends invited the whole class over for a mega-awesome party. Complete with this giant inflatable waterslide.
Little Man wouldn't touch it with a ten-foot pole. Sweet Pea went down once, came out crying, and was done with the water slide. But they still had a blast with water balloons, snacks, bubbles and general four-year-old craziness.
Direct link to video: https://youtu.be/2D__2YFNlcA