Hello lc215,
Thank you for reaching out in Apple Support Communities. We understand you'd like to know, where the family organizer can accept a child into Family Sharing. We can help point you in the right direction.
The family organizer in which the child is being transferred to in Family Sharing will receive a notification to approve the request. From there, the family organizer can go on an iOS device or a Mac to approve the child. For the appropriate steps is outlined in the section of this article that says, "If the child is already in your family": Move a child to another group using Family Sharing
Please let us know if that helps.
Kind regards.