C&C (not nitpicky) per request:
A number of good points have already been made, so I'm going to focus on the compositions of these. First off, good job getting down to her level.
I feel the first shot is cropped way too tightly. Frankly I think I'd feel this shot would be a bit claustrophobic even with an adult model, but for children you generally want to leave more open space in the frame to play off a child's sense of adventure and exploration. They have their whole lives ahead of them, give them room in the shot to grow into. This was shot outdoors, and even though she's not smiling as much as in the second shot she's still in a good mood - contextual clues that suggest the shots wants more breathing room. I'm not saying you can never crop a child closely - a shot of a sullen kid sitting in a corner in timeout may certainly be appropriate for a close crop.
For the second shot, I think you could have cropped just a touch more closely to make her a slightly larger portion of the frame, but not by much. Particularly in relation to what I said about the first shot, I like the open feel of this one. I like how you included a bit of the sky (and did not let the horizon cut through her head). The biggest drawback to the composition here IMO is that she is very centered both horizontally and vertically. I think with her pose (square to the camera, centered on her blanket) you can get away with keeping her horizontally centered, but if you had moved her up or down in the frame the shot would be stronger.
One final question - what kind of reflector were you using? You'll get different results from a translucent white disc than you will from a solid white reflective cover (or a silver or a gold reflective surface).