Kids can sometimes be hard to photograph, they don’t like to hold still. Here is something that has worked for me when I am in a tough spot. It can work for anyone as long as they have one or two off camera flashes.
Just hand them the flash and start shooting. Maybe give them a little direction so they don’t point it right at their eyes. As you can see a lot of the photos do not work but then on occasion you will get on with the right expression.
I find that because the kids tend to move around a lot it is best to shoot wider than normal and then crop in when you have the photo that works.
The beauty of flashes is that they can automatically correct for exposure. Give it a try. Have fun!