In order to buy life insurance on another person, you need an "Insurable Interest" in the person you wish to insure.
Insurable Interest does exist between parents and their children.
Insurable Interest means you either rely on that person for financial sup[port of some kind, or that you would suffer some form of financial loss if the person you wish to insure were to die.
Parents usually pay for their child's burial, funeral or cremation, and would therefore suffer a financial cost upon the passing of their child.
This is just one example of the insurable interest that exists between parents and their children.
Learn more about buying life insurance for your children.