I don't think small sellers have anything to do with child labour. And since you mentioned loopholes, it is always the big players who get away with loopholes that small business owners do not
Small sellers aren’t worth even going after until they reach a certain size for huge swaths of the regulatory regime.
See, for example, UL/CE and FCC regulations - unless they burn something down or interfere with emergency services, businesses can usually defer the regulatory cost till they can afford it. Or the FAA, which gives out slaps on the wrist like its going out of style, as long as the offender is not an airline.
Case in point: many countries allows underage family members to work for family businesses and even the ones that don’t, barely enforce it. A factory hiring dozens of kids? That’s a lot less likely to go unnoticed.
Business owners get away with breaking violating the law. Small businesses are infamous for paying people under the table, stealing wages, not giving appropriate breaks, employing children etc.. The size of a business only affects the kind of laws they're likely to get away with breaking.
