Disable Family Sharing for Apple TV+
Assuming that you’re using parental controls on your child’s iPad, you can disable access to video content with the ratings of your choice. See here for Apple’s instructions on how to do so.
The current instructions (which may change, so following the link is preferable) are:

To restrict explicit content and content ratings:

Go to Settings and tap Screen Time.

Tap Content &amp; Privacy Restrictions, then tap Content  Restrictions.

Choose the settings you want for each feature or setting under Allowed Store Content.