Family sharing
If I sign up for Apple Music on my family share account will my children’s Apple Music @ 9.99 a month be cancelled
iPhone XS
Question marked as
If your children are using their own Apple ID, and are part of a family group with Apple Music family subscription., then yes. It will automatically cancel the renewal of their Individual subscriptions when the Family subscription is activated.
See here: Get an Apple Music Family subscription - Apple Support
You can verify the subscription status, once the Family Subscription is active, by following the steps here, from the children;s devices: View, change, or cancel your subscriptions - Apple Support