✔ 最佳答案
youngster--------child; youth; young person
e.g. How are your youngsters (i.e. your children)?
teenager--------a person with the age from 13 to 19;
a person in his or her teens
THERE IS NO BIG DIFERENCE BETWEEN THE USAGE OF YOUNGSTER AND TEENAGER. THE ONLY DIFFERENCE IS YOUNGSTER MAY MEAN A WIDER RANGE OF AGE, I.E. BELOW THE AGE OF 25 SOMETHING.
參考: I hope my answer is helpful.