I hope you know that stuff used to be legal in the US well into the 70s. In fact, it wasn't even outlawed until 1977 with New York v. Ferber and the Protection of Children Against Sexual Exploitation Act of 1977. Prior, you could purchase magazines and films of children, especially young boys, engaging in sex acts from sex shops or traded publicly with street vendors. They usually went under names like "Nudist Moppets" or "Bambina Sex" and it was typically produced in Europe. It wasn't until 1976 when Robin Lloyd of NBC wrote the column "For Money Or Love: Boy Prostitutes In America" which was when Judianne Densen-Gerber of the Odyssey home drug treatment program used that publication to shape public opinion on it and launched a campaign to criminalize it, with media outlets like the New York Times and 60 Minutes reporting on it as well. Then that same year, House Democrats Dale E. Kildee of Michigan and John M. Murphy of New York banned it in their respective states under their state obscenity laws. Then the next year, Paul Ira Ferber got busted for selling videos of two underage boys masturbating to undercover police officers so he took the case to the Supreme Court arguing that it was free speech, that other depictions of dangerous activity weren't prohibited and that CP laws even prohibited materials that were not necessarily legally obscene in themselves. He lost, and it was banned nationwide by Congress/the Supreme Court under their 1977 law which made it 16+ to perform in a pornographic film.
Then in 1984 you had the Child Protection Act of 1984 which made it 18+ to perform in a pornographic film. The media reports leading to it's criminalization were mostly exaggerated or even erroneous, mostly revolving around the number of children involved and the amount of money being made. You used to be able to buy entire books with CP images in them for the same price as what a month's worth of internet bandwidth costs today, but thanks to legislators, that has changed. In fact, child erotica dates back to at least the 1400s.