The expression on her face, and the two boys, are very cute. However, I'd like to see more contrast. And with a special set of rules, take advantage of the full allowed size to really make an impact.
First off this is an adorable shot showing sibling love. Lighting is good and the color hues are soft in tone conveying a the mood of a tender moment. I like the added touch of the boy on the right holding his sister's hand. Compositionally this is good but could be even better. The reason? The boy on the right's kiss on his sister's head is lost behind her bow. And the boy on the right kiss is not as visible as it could be. Had both boys heads been in profile perfectly symmetrical on either side of their sister's forehead it would FURTHER capture a enduring moment where all facial features of everyone in the shot is wonderfully visible.
This has an old-time feel to it. She looks a bit overwhelmed. :-) To get maximum consideration from voters, use the largest size available to you. In this case we were allowed 720 pixels on the long side. If you're not sure how to resize, there's a tutorial under "Learn", or ask in the forums and someone can help you.