There is lots of conflicting evidence for the recommended sleep for teens. Much of it says 7-9 hours, others say up to 10 hours per night. However, both can be summed up to a basic range.
It is most optimal for teens to get 8-10 hours of sleep, and acceptable to achieve 7 hours per night. Any less and symptoms such as sleep deprevation, tiredness, and lack of focus can happen.
Children require more, with youth school aged children minimizing at 9 hours per night with no less than 8.
Younger children all the way to newborns require progressively more sleep, with preschoolers needing 10-13 hours, toddlers 11-14 hours, and 12-15 hours for infants less than one year old.
More detailed set of ranges can be found on https://sleepfoundation.org/