What type of life insurance product can extend coverage to children under their parent's policy?

The correct choice is the term rider, as this type of product is specifically designed to add coverage for dependents, such as children, under a parent’s existing life insurance policy. A term rider provides a temporary and additional life insurance benefit that is often less expensive, allowing parents to secure coverage for their children without requiring a separate policy for each child.

Whole life policies, universal life policies, and variable life policies typically focus on insuring the primary policyholder and may include features like cash value accumulation or investment opportunities. While some of these policies might allow for child riders, the primary feature of the term rider is the straightforward addition of coverage for a specific term, which aligns directly with the needs of providing life insurance for children. Thus, it is the most fitting option for extending coverage to children under their parent's policy.