Especially with younger children, the lower you can hold your phone the better they will look in the photo.
At a minimum try to hold the phone at their eye level for a clearer and more detailed shot of their faces. Or go the extra mile, like this photo, and shoot from the ground.
It also gives you a better chance to follow two bonus rules:
1) never cut off feet; and
2) have the ball in the shot.
Looking up to your players, rather than down, also makes for more engaging team shots.