Mo. Rev. Stat. § 306.122

No person under fourteen years of age shall operate any motorboat or vessel upon the waters of this state unless such person is under the direct on-board supervision of a parent, guardian or other person sixteen years of age or older, or unless the motorboat is moored. No person shall authorize or knowingly permit a motorboat owned by such person or under the person's control to be operated on the waters of this state in violation of this section, nor shall a parent or guardian authorize or knowingly permit such a child, under fourteen years of age, to operate a motorboat in violation of this section.