In Family Setup, The following features and apps are not available: Medications, respiratory rate, irregular heart rhythm notifications, ECG, AFib History, Cycle Tracking, Sleep, Wrist Temperature, Blood Oxygen, Walking Steadiness, Audiobooks, Remote, News, Shortcuts, and the double tap gesture.
https://support.apple.com/en-us/HT211768
Since sleep tracking isn’t supported, you’ll probably have to reset it to get the sleep app to show up.