They just need to fall asleep
"Today nobody brought his or her instrument" is correct. It is common for people to use "their" in a sentence like this, but "his or her" is the more proper term.
Twain is informing people aboutn how young kids are being pushed to do things they dont want to do. As in peer preasure, cleanrly this young boy should not be smoking or chewing tabacco but he tries because of the people laughing at him about not being able to chew tabacco. Mark Twain is conveying a former problem that we still have but do not acknowledge anymore. This happening will not just affect an individual, but everyone around.