Don't check with your goddamn wrists

"Checking" in ice hockey usually involves full-body contact. The mom is telling the players to go at it without holding anything back.

While there are several kinds of checking, involving different parts of the body, the mom is referring to "full-body checking."

According to the USA Hockey rulebook website:

A hard body check or using body contact/position (Body Contact categories) to gain a competitive advantage over the opponent should not be penalized as long as it is performed within the rules. The focus of the body check should be to separate the opponent from the puck.