Mo. Rev. Stat. § 431.060: Contracts by persons under eighteen years of age — ratification necessary — how made.

No action shall be maintained whereby to charge any person upon any debt contracted before such person becomes eighteen years of age, unless such person shall have ratified the same by some other act than a verbal promise to pay the same; and the following acts on the part of such person after he becomes eighteen years of age shall constitute a ratification of such debt:

(1) An acknowledgment of, or promise to pay such debt, made in writing;

(2) A partial payment upon such debt;

(3) A disposal of part or all of the property for which such debt was contracted;

(4) A refusal to deliver property in his possession or under his control, for which such debt was contracted, to the person to whom the debt is due, on demand therefor made in writing.