Yes you can buy burial insurance on your parents, although some life insurance carriers may require that the insured pay the premiums.  

Otherwise, you as the owner of their burial life insurance policies may be able to pay the premiums.

It is usually fine for the adult child to own the insurance policy and be the beneficiary of the policy, too.  

Most of these burial insurance policies do not require your parents to take any medical exam, but may require the proposed insured to...