Can my child’s friends be included on a family travel insurance policy?

A Single policy can cover one adult traveller on their own, or one adult together with their dependant children or grandchildren. Even if your children are listed on the policy, it will still be issued as a Single policy because you are the primary insured adult. 

As long as your children meet the dependant definition aged 20 years and under, not in full-time employment, and travelling with you for the entire trip, they will be covered under your Single policy.