If you are a provider booking an appointment with a child of a parent, just select the child you want to book with and schedule that way, however all notices will go to to main account holder which in most cases it is the parent. You would only select the parent if you wanted to book and appointment with the parent. Sometimes the child and parent take lessons from the same provider.
If you are a parent in some cases it makes sense to create an account under your child's name and their own email, since a Fons account can only have one email address associated with it at a time. If your child is in charge of handling their own communication and appointment scheduling, then it would make more sense for them to use their email instead of their parent's.
Please Note: All scheduling AND payment notifications will go to the email address on file with Fons. Be sure to check in with your child about billing notifications if they are in charge of their own scheduling, but not their own billing.