Maybe you did not pay attention to the original post, but no 4 or 6 year old is going to wear a hard nightguard. Soft nightguards only make things worse.
KLT83, grinding in children is nothing to worry about. Their mouths are going through constant changes (jaws growing, losing teeth, getting new teeth) and the grinding is the body's way of trying to balance everything. Most children stop once a majority of their permanent teeth are in because they develop a healthy tooth balance. If they do not, braces will help starting at age 10-12.
First tell the kids to stop doing it, especially if it's during the daytime hours. My 16 yo does it in the car and I tell her to stop it immediately. Also a night time appliance like a night guard will help support the TMJ's during his development. Untreated bruxism in kids generally will not cause long term problems but as a preventative, a night guard could be considered.
mouth guard is an appliance used in a patient with bruxism, it is used for prevention so that their tooth will not be abraided
Bruxism is common among children. There is no known deleterious effect. Treatment is generally not indicated.