OK ... for a 3 year old:
Great image!
Cute little girl!
You did good 
I like the colours, and the lighting is very nice in my opinion. Plus, your subject is stunning!
Don't know whether the composition could be improved by applying the rule of thirds (e.g. cropping out the right fence), but you could experiment. (EDIT: Hehe, Lomond beat me to that one
)
It might be nice to have her legs in the image, as stated, but I find that the image is exciting for me that way. I like tightly cropped images 
I find the bokeh (out-of-focus areas behind here) a bit choppy, but not really bad ... maybe applying just a bit of Gaussian blur to the background might make the picture more quiet. If you want to read up on the issue, look here.
Still, I think the picture is wonderful as it is
.
Best regards,
Andy