Capitalism requires a reserve army of labor in order to function. Bosses need a steady supply of unemployed people in order to suppress wages and maintain the threat of termination. If workers can be readily fired and replaced, capital wins.
If you know a 14-15 year old discourage them from taking extra hours if offered. Let them know their free time is valuable. Basically anyone under the age of 18 is constantly told they're lazy and have it easy, which isn't the case. Middle and high school already take up a ridiculous amount of students' time, it's a sacrifice for them to take on work at all.