Mo. Rev. Stat. § 115.409
Except election authority personnel, election judges, watchers and challengers appointed pursuant to section 115.105 or 115.107, law enforcement officials at the request of election officials or in the line of duty, minor children under the age of eighteen accompanying an adult who is in the process of voting, international observers who have registered as such with the election authority, persons designated by the election authority to administer a simulated youth election for persons ineligible to vote because of their age, members of the news media who present identification satisfactory to the election judges and who are present only for the purpose of bona fide news coverage except as provided in subdivision (18) of section 115.637, provided that such coverage does not disclose how any voter cast the voter's ballot on any question or candidate or in the case of a primary election on which party ballot they voted or does not interfere with the general conduct of the election as determined by the election judges or election authority, and registered voters who are eligible to vote at the polling place, no person shall be admitted to a polling place.
§ 115.409, RSMo