I like your question very much Kelli. I think one of the reasons that adults just don’t let go and have fun has alot to do with “keeping up appearances.”
I think it is important to find out what brings the kid out in an adult and include that as part of your fitness programming.
I feel like a kid again when I put on my Kangoo Jumps and jump. I feel like a kid again when I am playing with my son or surrounded around young people who like to play.
I wish I could pinpoint exactly what it is that makes adults feel that horsing around is a big no no. However, I think people in general would be happier if they played more.