The youth size Shock Doctor mouthguard in purple is only $3.86 on clearance from $12.99. If your kids are like mine they chew on their mouth guards and go through them quickly. Picking up 6 of these with free store shipping as stocking stuffers.
The blue one is $5.81 if you are worried about the color.
You can probably price match and add this to your order at Dick's Sporting Goods for Cyber Monday too.