U.S. laws protect child workers. But the laws are different for different kinds of jobs. For example, there are fewer limits on the work children can do on farms. What do you think?

What do you mean by "fewer limits"?

The laws are basically ... Children can't work on farms.  (except family farms)  At least in Oregon/Washington - which is why the farms have to rely on migrant workers now, rather than paying middle/high schoolers to pick crops as they did when I was growing up.

The labor laws for farms are similar to other labor laws, ESPECIALLY when it comes to child labor laws. They are a bit loser for agriculture (not just farms) then it is for other industries, but not much. About the only actual law I know of, for sure, is the overtime law.

The only way a child can work on a farm is if it is a family farm. Children are given chores to do and it is often th only way a family farm can function. Plus the laws were writtien when there were a lot of family farms. It was vital to feeding our country. There are rules as to what they can do on the farms. There are age limits as to whether they can work any farm equipment. 

At the time the laws were written to keep children from working in factories. They were cheap labor who were not going to complain about horrible conditions. They were often maimed or killed. The laws were written to protect them. It also allowed more children to go to school.