Ne-Waza “guard” question.

My son has been doing BJJ and Judo simultaneously. I have stepped away from Judo for a while.

The kids instructor at the dojo is telling my son not to do the “guard” or “spider guard” and that he can’t use his legs to prevent someone from pinning him.

I understand “stalling” is a disqualification or reset. During a judo competition.

Have you all seen instructions tell judokas to not use the guard or spider guard to prevent a pin?