Mo. Rev. Stat. § 475.345: Transactions of protectees voidable, when.

A sale, exchange, lease, gift, contract, release or other transaction affecting his estate entered into by a protectee at a time when he is a minor or lacks sufficient mental capacity to understand the transaction and its effect upon his estate, rights and future welfare is voidable at the option of the protectee or the conservator of his estate unless entered into with the consent of the conservator in the case of transactions which the conservator could enter into without court authorization under section 475.130 or with the authorization or approval of the court. The conservator is under a duty to treat as voidable transactions which are voidable at his option and not beneficial to the protectee or his estate.