Recently, I picked up Doraemon from an online bookstore. Doraemon was created in the 1970's. I noticed that a lot of Kanji did not have furigana on the side. This is interesting, because it was serialised in the kids' magazine CoroCoro Comic. I picked up a few more series, but these were created in the 90's-00's. They all had furigana for every Kanji that the characters used.

This is interesting. I'm really curious, was there a big change in attitudes, did the creators decide that they wanted to target a larger audience? Or did kids start learning Kanji later?

I've noticed that too. Even ARIA has furigana on every single kanji. Well, some manga were hand-lettered those days, and hand-lettering usually doesn't have furigana. But that can't explain all of them...

I think they want to target a larger audience. I am not sure how many versions of Doraemon there are (with and without furigana). Perhaps some people read Doraemon for nostalgic reasons?