Is a mouthguard required at 10U?

Not by rule at 10U, but it's strongly recommended.

• A colored (non-clear) internal mouthpiece covering all the remaining teeth of one jaw (usually the upper) becomes required at 12U and stays required through 18U, high school and girls' 19U.
• USA Hockey strongly recommends that every player at every level wear an internal mouthpiece, ideally one fitted by a dentist.