Since manga is not a genre but rather a format, one has to be very careful about selecting books - since most of the manga that is in print in English is actually for teenagers or adult readers. Finding kid friendly or "All Ages" titles takes work.
I have already mentioned how much my son and I like Twin Spica by Kou Yaginuma, even though the story is thoroughly packed with tragic backstories. Overall the series is amazingly sweet and hopeful. We are impatiently waiting for volume 5 to show up in the mail. The books are out of print, so I have been tracking down copies and they are arriving out of order. It is rather tough to have volumes 6 and 7 sitting there, giggling at you, while you have to wait for 5 to turn up. So far though the story is very worth the effort.
From the back of volume 1:
Chi is a mischievous newborn American shorthair who, while on a leisurely stroll with her family, found herself lost. When we found Chi it was clear to us she was completely distraught as she longed for the warmth and protection of her mother. Feeling sympathy for the little fur ball, we quietly whisked her away inviting her into our small apartment home … where pets are strictly not permitted. While we dread parting with her, there is no way she can stay.
Little Chi is a happy and healthy litter-box trained kitten. And while she can be a little bit of a handful, she has been a great source of joy in our lives and a wonderful companion to our young son. Living with Chi has completely changed our lives, and we are sure she will have the same impact with whomever gives her a good home.
よつば - translates as "four leaved clover." よつば is the five year old adopted daughter of Mr. Koiwai - a single father who is portrayed as a bit of a slacker with a strangely laissez-faire attitude about his daughter's activities (like he knows she is going to be safe no matter what - it's rather hard to explain). Unlike Twin Spica (but similar to Chi's Sweet Home) there is no overall story arch. Instead, each of the stories is simply about Yotsuba learning something about everyday life - she is strangely naive about things that most children are well acquainted with - like how to use a swing or what door bells are for. The title comes from how the chapters are named "Yotsuba & something," where something is the new thing or concept she encounters that day (the first chapter is called Yotsuba & Moving), and the exclamation mark comes from her way of throwing herself enthusiastically into everything she does.
Apparently the stories were originally written for a more mature audience (it was originally published in Dengeki Daioh, a magazine intended for teen boys or adult men - there are conflicting descriptions of this - suffice it to say that American parents would be rather put off by the source) so there are a few occasional surprises in the language or behavior of the adult characters - nothing too bad and stuff that will sail right of the heads of children - just briefly off-putting for any adults reading the stories with their younger children. Definitely nothing that has struck me as totally inappropriate.
The interesting thing about Yotsuba, and Chi, is that the stories manage to capture the perspectives of both the innocent (like Chi and Yotsuba) and the adults around them. 'Slice of life is really' a good way to describe them.
This is the description from the back of the first volume:
Hello! This is Koiwai Yotsuba, Yotsuba Koiwai…um, YOTSUBA! Yotsuba moved with Daddy to a new house from our old house waaaaaaay over there! And moving’s fun ’cos people wave! (Ohhhh!!) And Yotsuba met these nice people next door and made friends to play with (one of ’em acted like one of those bad strangers Daddy told Yotsuba not to go with, but it was okay in the end). I hope we get to play a lot. And eat ice cream! And-and-and…oh yeah! You should come play with Yotsuba too!
From the back:
In the far future, war has destroyed the entire Earth, leaving only a barren wasteland where the supply of water is controlled by the greedy king. In search of a long-lost lake, Sheriff Rao asked the king of the demons for help ... and got the king's son, Beelzebub, and his assistant, Thief. Together the unlikely trio sets off across the desert, facing dragons, bandits and the deadliest foe of all ... the King's Army itself! It's travel adventure and tank action in this new story from Akira Toriyama, the creator of Dragon Ball Z!