I think one can look at this shot in two ways: 1) the relationship between the girls and the setting (how they blend in being covered in so much of that setting!), or 2) a portrait of two muddy kids. If it's the former, perhaps a wider shot would be in order, just to provide a bit more context and sense of place. If it's the latter, then I would like to see a closer shot of the girls - compose for a head-to-toe or maybe even a head-to-waist shot.
This photo is also washed out and could do with a bit of contrast. I'm not sure what colour the soil is at the "track", but it appears pink in this photo, which is a bit odd (to me, anyway). I tweaked it a bit in PS - I hope you don't mind. In the end, it's quite a unique moment and a funny scene. Glad you shared it. :)