Protecting Our Kids Act This bill makes various changes to federal firearms laws, including to establish new criminal offenses and to expand the types of weapons and devices that are subject to regulation. Among the changes, the bill generally prohibits the sale or transfer of certain semiautomatic firearms to individuals who are under 21 years of age; establishes new federal criminal offenses for gun trafficking and related conduct; establishes a federal statutory framework to regulate ghost guns (i.e., guns without serial numbers); establishes a framework to regulate the storage of firearms on residential premises at the federal, state, and tribal levels; subjects bump stocks to regulation under federal firearms laws; generally prohibits the import, sale, manufacture, transfer, and possession of large capacity ammunition feeding devices; and requires the Department of Justice to report on the demographic data of persons who are determined to be ineligible to purchase a firearm based on a background check performed by the national instant criminal background check system.