In order to do this post properly, I'd need a huge collection of every edition of various economics textbooks. Because I don't have that sort of collection, I'll rely on second hand sources and hope for the best. Please correct any errors you find.
In the third edition of Mankiw's excellent textbook, he quotes Paul Krugman defending child labor (as a lesser of evils) in the context of international trade agreements:
Could anything be worse than having children work in sweatshops? Alas, yes. In 1993, child workers in Bangladesh were found to be producing clothing for Wal-Mart, and Senator Tom Harkin proposed legislation banning imports from countries employing underage workers. The direct result was that Bangladeshi textile factories stopped employing children. But did the children go back to school? Did they return to happy homes? Not according to Oxfam, which found that the displaced child workers ended up in even worse jobs, or on the streets -- and that a significant number were forced into prostitution.
That all seems pretty unobjectionable to me. Who favors child prostitution? (Apparently, lots of people favor policies that lead to child prostitution.)
I'm told that this Krugman comment was removed from later editions. In the 4th edition it was replaced with an article by Virginia Postrel, which emphasized that most parents don't want their kids to work, and that economic growth was the most reliable way of eliminating child labor. Once again this is very sensible, and perhaps less controversial. I'm told that still newer editions also dropped even that discussion.
I'm also told that another popular textbook by Hubbard and O'Brien had a defense of child labor, which was removed in later editions.
Now I'm working on my own textbook. I had included some comments similar to the Krugman quote above, and got so much pushback from various sources that it had to be deleted before the book was even published. I don't want to make too much of this in terms of the textbook, which I still think will be excellent. We can work around these minor issues. I'm more worried about what it says about the profession. (Textbooks reflect the preferences of the professors that require them, not the students that buy them.)
I'm really happy that I lived through the 1980s and 1990s, which was a sort of golden age of economics. As I get older (and grouchier and more reactionary), I am increasingly dismayed to see economics enter a new dark age, sort of like 1930-66. I doubt I'll live long enough to see the end of this one, but younger free market economists should not lose hope. Truth always wins out in the long run. (A cynic would say, "Yeah, that's mostly because, as Richard Rorty pointed out, truth is sort of defined as what wins out in the long run.")
Eventually the field will come back to its senses.
PS. The new textbook will utilize "never reason from a price change" as a teaching tool for prices, interest rates and exchange rates.