The amount of sleep your teen is getting and the regularity of their sleep schedule is most important, so sleeping until the late morning may actually be okay.
Teenagers become night owls during puberty
My teen is sleeping all day, should I be concerned? - Children's National
Sleep for Teenagers
When a teen's tiredness signifies a serious health problem
The Importance Of Sleep For Kids: Sleep Services of Maryland LLC: Sleep Medicine
Why is my teenager sleeping so much?
Dangerous Kids' Symptoms You Should Never Ignore
Why Is My Teen Always so Tired? Do They Have Depression?
The 3-Year-Old Sleep Regression in Toddlers
9 Things You Need To Know About Naps
How Much Sleep Do You (& Your Kids) Really Need Each Night? — Baby2Body
Don't be a Grinch — but heed this advice if you want your kids to sleep on Christmas Eve
My Son Sleeps All Day and Is up All Night” - Parents Ask