A ten-day 'mud and nature' camp for 3 to 5 year olds. Worth paying for?

The flyer promises gardening, clay, water play and 'sensory exploration', two hours every morning for ten days in May. Our son would love it. He already does most of this in the park downstairs with a spoon and a bucket, for free. What I'm really weighing is the company. He's at home with us all summer and misses other children. Has anyone tried a short camp like this at 3 or 4? Was it the activities or the other children that made it worth it?