The Wikipedia help page, Advice for parents, is provided to help parents, guardians, teachers, and other adults consider the best way to allow children they are responsible for to engage with Wikipedia safely and enjoyably.
The most useful piece of advice guardians can give to younger editors is to never divulge any personally identifiable information (name, age, location, school) on Wikipedia—or anywhere else publicly available on the Internet for that matter. Wikipedia is not censored, and contains explicit material and images. Parental controls may be able to help.
You may also be interested in another independent project, the Schools' Wikipedia—a specific selection of about 5,500 articles from the English Wikipedia, suitable for school children, which has been checked and edited for this audience.