Someone in any form of work can feel exploited. It's all a state of mind. And there we have it. Exploitation is a matter of feelings. To be honest, I should be careful dismissing feelings as the key to exploitation.
Feelings are relevant and historians risk hypocrisy by denying it outright.
The children don't think they are being exploited. They think they're doing something that will get themselves and their families food and shelter. It's not just kids. Some of those better trained in the psycho-babble sciences, call it denial. But the facts are the same.