I found this, not as strict as MS regulations.
All vessels 16 feet in length or longer must carry onewearable USCG–approved PFD (life jacket) for each personon board or being towed. Vessels less than 16 feet in lengthmust carry one wearable or one throwable USCG–approvedPFD for each person on board or being towed. Underfederal law, however, a wearable PFD is required for eachperson on board regardless of vessel length.■ Children under 7 years of age must wear a USCG–approvedPFD at all times while on board any vessel, unless the childis confined in a totally enclosed area of the vessel, such as thecabin area of a houseboat or day cruiser.