Mo. Rev. Stat. § 475.025
In all cases not otherwise provided for by law, the father and mother, with equal powers, rights and duties, while living, and in case of the death of either parent the survivor, or when there is no lawful father, then the mother, if living, is the natural guardian of their children, and has the custody and care of their persons and education. When the estate of a minor is derived from a parent, the parent as natural guardian has all of the powers of a conservator appointed by a court, with respect to property derived from him, except that no court order or authorization is necessary to exercise these powers and the natural guardian may invest, sell and reinvest the estate of the minor in such property as is reasonable and prudent.
§ 475.025, RSMo