Nice shot, and very brave of you to enter a challenge with not just 1 kitten, but three!
The way they're lined up makes for a good composition, it's just a shame the quality of light isn't better... the light seems to be highlighting a couple of leaves in the bottom-left of the frame. The dof is just too shallow which is a shame, as the kitten on the right needs to be a bit sharper.
I think the fact that your background consists of a lot of leaves means that there's a little too much here in the way of detail and texture for the eye to really settle on the kittens, and this is why this photo has a bit of a snapshot feel to it.
But you've captured a nice feel here, and this photo is a great record of these kittens' first foray into the outside world.
This is the kind of photo that could be on every calendar everywhere. This is an awesome capture of expression - and, of course, those kittens are just about the sweetest things I've ever seen in my life. The coolest part is that there's a lot of humour in this photo - it's well composed. The only comment (and this is very minor) is that you may want to increase the saturation just slightly - the greens are dead-on, but you may want to try to enhance the leaves slightly - and maybe the orange of the kittens. It's a 10 though and you should be proud.