My parents think that reading comic books helped my sisters and I learn Japanese when we were young. I remember reading Sailor Moon(セーラームーン), Chibi Marikochan(ちびまる子ちゃん), Rayearth(レイアース), and Doraemon(ドラエモン). (P.S. By the way, sisters, whoever has Sailor Moon and Rayearth, I bought those with my $ so I want them back!)
I think out of all of those comics, Doraemon is the most universally appealing series. It is geared towards both girls and boys, the storyline is easy to understand even if you haven’t lived in Japan, and unlike some other comics, you don’t have to buy multiple books to find out what happens in the end. I don’t think it has any “iffy” content that parents have to worry about. I think it is a great comic for elementary-aged children.
If you want to read Doraemon, you just have to click over to Dora-world.com’s comics section and you can read several interactive chapters for free! The website also has a lot of printable coloring pages, a “secret” fourth-dimension channel where you can watch short animated episodes, and probably more stuff if you click around. You can watch old episodes online:
P.S. Have you seen the last episode of Doraemon?