This makes me smile, as so many of your shots of the folks you work with do! Great smiles on the kids, and it's easy to see everyone had a good time with this.
Not really a stock image and has a snap shot feel to it.
Your inner boarder looks like it was produced from a layer with transparency, now I'm not sure but I don't think you can do that within Basic. I'm not reporting it or anything childish like that but it may be worth checking for next time.
As far as the image goes it has a nice range of vibrant colours that work well together.
A good candid utilizing the theme of spontaneity which is unforced and unplanned. Shows a willingness to keep fit. Good detail and pleasant smiles work well. Not a perfect reflection on the challenge theme, but a good solid effort.
Fitness? Sure. Stock photo? No way. The background is very disstracting, the lighting is a bit harsh, I don't care for the border... They're adorable kids, but there's a lack of attention to details in this snapshot.