What are the reasons that young people might need sedative pills?

How young?: "Sedative" is a very broad description as is "young". You'd need to be much more specific about what meds and what age.

Sedative rx and age: Sometimes a nervous child will benefit from benadryl, (diphenhydramine) per pediatrician only. Sometime a sick child will benefit. Teens and twenties and thirties and forties are better without sedatives, and should not seek sedation artificially. Certain illness contexts may call for a sedative short term, but that is a doctors judgement. Much better it is to be natural with our body rhythms and sleep cycles.

Need more info: need medical history, age, medication......in order to answer. If you are the parent or legal guardian and the peron is under 18 you can discuss it with their doctor.