Mo. Rev. Stat. § 376.820: Insurers may not deny coverage of child because of marital status of parents, residence or income tax dependency claim.

No individual or group insurance policy providing coverage on an expense-incurred basis, no individual or group service or indemnity contract issued by a not-for-profit health services corporation, no health maintenance organization nor any self-insured group health benefit plan of any type or description shall be offered, issued or renewed in this state on or after July 1, 1994, by an insurer, including a group health plan, as defined in section 607(1) of the federal Employee Retirement Income Security Act of 1974, that denies enrollment of a child under the health coverage of the child's parent on the grounds that:

(1) The child was born out of wedlock; or

(2) The child is not claimed as a dependent on the parent's federal income tax return; or

(3) The child does not reside with the parent or in the insurer's service area.