What did the Human Rights Watch report say about children who work on tobacco farms? How are the restrictions on child labor in agriculture different from the restrictions in other industries?

Part 1 of your question see this site

https://www.hrw.org/news/2014/05/14/us-child-workers-danger-tobacco-farms

Part 2, you must first define what you consider "Child Labor".  Is a child collecting eggs each morning for his mother, as that is his chore, child labor?  Are kids who raise and care for animals as part of their 4H club  doing child labor?  Is a teenager, driving a tractor to help his or her father get the crops off child labor?