There was a lesser known release of Kodocha as an OVA in 1995. It basically manages to cover the first manga volume in half an hour. Yes the whole thing in half an hour. While faithful to the manga, it tends to have a bit of a darker feel.
Kodomo no Omocha was produced as a TV series that aired for 2 years, and is generally what the series is known for. While it keeps the general storyline, the TV series truly took on a life of its own. In particular a lot of comedy was injected to keep a fairly light atmosphere and changes the feel of the series a bit. The first two seasons were released by Funmation in the U.S. as Kodocha, but unfortunately the other 60 or so episodes won't be licensed due to poor sales. This page is mostly dedicated towards the TV series.
Kodocha is the story about a girl named Sana and her various escapades and interactions with a boy named Akito. At the start of the series they are age 11 and in elementary school. At first they were adversaries, later on becoming friends, and later still being involved in a sort of love triangle/pentagon. At it's core, Kodocha is more of a shoujo series, but also has a lot to do with relationships and just growing up in general.
Kodomo no Omocha was penned by Miho Obana. It was originally featured as a series in the popular shoujo magazine Ribbon for four years. Later, it was collected into 10 manga volumes. For a brief time the collections were also published in the U.S. by Tokyopop but is no longer printed or available. Overall the series was well received and won the Kodansha Manga Award for best shoujo series in 1998.