Hasn’t he admitted to changing his opinion after learning about the effects on children?

He did. The argument against him was half based on misquotes and incomplete sentences, but the other half was indeed once his opinion - he argued that age of consent was a dumb concept and that instead it should be based on what the child wants to do and any harm they were subjected to.

He later on said he regretted this view because it was explained to him that there's no ability to consent and this always causes harm to the child. His original arguments were, in typical Stallman fashion, quite obsessed with definitions themselves, almost as if the subject at hand didn't really matter he was just bothered about how the definition had some flaws.

But even with that in mind... I can't feel comfortable knowing he defended this point of view, and it does significantly harm my opinion about him.