It's the latest manga by Kiyohiko Azuma, the creator of Azumanga Daioh, although "latest" is slightly misleading since he started it over a decade ago. It's still running. There are twelve collected volumes out in Japan so far and it's been translated into English by ADV Manga and Yen Press.
No anime, though. Azuma doesn't think it would transfer well to animation.
It's about a little girl called Yotsuba. The Japanese title is "Yotsuba to", with the last syllable simply meaning "and". (It's like the Target novelisation title format of "Doctor Who and the [insert anything here]"). Yotsuba is young enough to have no clue about anything, but she doesn't care. Yotsuba enjoys the entire world, usually at the top of her voice. If it leaves her thunderstruck, that's all the better. She's like a small, loud force of nature, irrepressible in her willingness to do everything while understanding nothing. She'll enthusiastically agree to almost any proposal or request, although her attention span means that her memory of this might be swept away by some other equally wholehearted endeavour at any moment.
She's wonderful. It's impossible not to love the non-stop adventure that Yotsuba makes of her daily existence. She's passionately engaged with everything she sees and does. Everyone who knows Yotsuba is terribly fond of her. However she's an orphan whose faintly hopeless adopted father is the reason why Yotsuba comes across as somewhat "off the leash". She uses his faintly ugly speech patterns, for instance, which are normal from a graceless bloke and wildly inappropriate from a little girl. (This won't have come across fully in translation. I don't need to have read the English versions to tell you that.)
She has an unusual hairstyle, incidentally. It's like a sea creature on her head, sticking its legs in the air. However this is explained by Yotsuba's name, which means "four-leaved" (as in four-leaved clover) and her hair reflects that.
That said, the manga didn't come across quite as I'd expected.
Firstly, it's not Just William. It's not set in a child's world and I wouldn't even say that it's being viewed through a child's eyes. Yotsuba's being portrayed more dispassionately than that, while the rest of the cast are either adults or at least older than Yotsuba. In some ways, Azuma's giving a fuller portrayal of childhood than I'd expected. Yotsuba will be terrified of odd things (big eyes), she has a child's utter dependence on adults and she can be crushed or driven to a near-meltdown when the world betrays her. (This might include her own inability to do something.) Her most important relationship isn't with a friend her own age, but with her father.
Secondly, a surprisingly large amount of it isn't about Yotsuba. The other characters include her father, their friend Jumbo (who's about eight feet tall) and the family who live next door (Asagi, Fuka, Ena, their mother and occasionally also their father). To be honest, the early chapters flag a bit when they're focused on the adults. None of them come across as particularly interesting, despite the men's oafish eccentricities (which explain a lot about Yotsuba), although they settle down and improve later.
As for the art, it's nice, clean and simple, making for an ideal match of style and content. Azuma's typical manga freedom with facial expressions is probably better suited to portraying Yotsuba and her world than a less impressionistic style would have been... although that said, it's only people's faces that are simplified and that's for emotional impact. There's plenty of realism in the backgrounds and figure work. The level of detail is often impressive, actually.
Oh, and it's also easy to read if you're learning Japanese. Yotsuba conversations are simple, easy to follow and don't get bogged down in obscure kanji or high-flown subject matter.
Is it good? Yes, very. It had already been on my "to read" list when someone, unprompted, told me it was one of his favourites. What's more, I've only read the first three volumes and I understand it gets better and better as it goes along and Azuma relaxes properly into what he's doing. I can see that. As the chapters go past, I can see myself getting fonder of the cast and their foibles. However the heart and soul of the manga is, of course, Yotsuba. She's been making me laugh right from the beginning and it's both charming and refreshing to be with her as she sees so many things for the first time. It's sometimes a bit nerve-racking, too, of course. Yotsuba is accident-prone and not excessively gifted with social graces, so one gets a bit itchy seeing her unleashed in certain situations. It's a good kind of nervousness, though. I really rather like this one.