It’s pretty well-known at this point, I thought? Regardless:
“The nominee is quoted as saying that if the choice of a sexual partner were protected by the Constitution, ‘prostitution, adultery, necrophilia, bestiality, possession of child pornography, and even incest and pedophilia’ also would be. He is probably mistaken, legally–but that is unfortunate. All of these acts should be legal as long as no one is coerced. They are illegal only because of prejudice and narrowmindedness.”
RMS on June 28th, 2003
"I am skeptical of the claim that voluntarily pedophilia harms children. The arguments that it causes harm seem to be based on cases which aren’t voluntary, which are then stretched by parents who are horrified by the idea that their little baby is maturing. "
RMS on June 5th, 2006
"There is little evidence to justify the widespread assumption that willing participation in pedophilia hurts children.
RMS on Jan 4th, 2013
You can find these on Stallman’s blog, which I believe is Stallman.org iirc. Just go to the dates I provided.