[solved] According to the ethical relativism school of thought,

whether the use of underage labor is ethically acceptable or not hinges upon the ethical standards that each industry establishes for its member businesses.

it is very clear and well-established that the use of underage labor is ethically impermissible, even in those countries and situations where it is the local custom to utilize child labor.

if the use of underage labor is acceptable in a particular culture/society/country, then it is ethical for a company to use underage labor in conducting its business activities in that culture/society/country.

if the use of underage labor is legal in a particular country, then it is ethical for a company to use underage labor in conducting its business activities in that country, no matter what the legality of using underage labor happens to be in other countries.

it is up to each business to set its own standards for deciding whether the use of underage labor is ethically acceptable or not.