Window lighting can be tricky and irritating. One thing I've found to be very helpful is to set your subject up about 3 feet from a window that doesn't receive direct sunlight. Thats not the tricky part.
The tricky part is fooling your camera meter so that it doesn't see a huge white area near the window that is flooded with light (metering off that light) and seeing the skin tone of your subject and metering off your SUBJECT.
So what you do is go up to your subject, like seriously right in their face, and fill your frame with just them. Take those settings and use those, forget what your camera thinks you should use at a distance, switch it to manual and force it to take the picture at what it thought your subject should be shot at when it was inches away.
Then, bracket a few shots. Shoot a few at 1 and 2 shutters higher / lower and then choose which is best once you see them all blown up.
This is also a great method for when you want to shoot your subject inside a window. Typically your camera would meter the huge white space behind your subject, but if you get right in their face and meter your subject and just your subject (neglecting your background) and shoot it at those, you'll get a nicely overexposed background, but your subject will look perfect.
Most subjects in kindergarten don't let you get away with this, but you're looks like an exception, so give it a try and let me know if it helped
