Child labor laws apply no matter what, regardless of stock, who owns the company or what the employment circumstances of the child are.
Food business, shops, and manual labor jobs
Child Labor is very complicated. Therefore the same rules do not apply in pennsylvania.
Nearly every billion dollar shoe company uses child labor.
Nike and Walmart
The company cannot require you to have your children to work. If the parent brings it home and has the child do it, that is their decision, but they might be subject to child labor laws.
It depends on the country where they use child labor, and what kind of rules the country has about it. If the laws don't let you use child labor then the company is using children illegally.
Walmart
The labor laws of the state in which you work are the ones that apply to you. If a company is headquartered in one state, you live in another state, and work in still another state, the state you work in has jurisdiction.
Child labor
I don't know about restrictions that would apply, but your policy or the issueing company should be able to answer this for you.
It depends on labor laws and any union/employment agreements/contracts that apply to the company or where you live.
A socially responsible consumer might boycott a company that uses child labor.