Short answers, pulled from the story.
Children's anime and manga refer to manga and anime directed at pre-adolescent children. These works are usually moralistic, aiming to guide children toward the right path in life, and each chapter is typically a self-contained story.
Manga aimed at children started in the late 19th century, with short works of approximately 15 pages printed in magazines. These were produced during the Meiji era as part of an effort to encourage literacy among Japanese youth.
Astro Boy was created by Osamu Tezuka, who is often considered the father of anime. The creation of Astro Boy marked a major milestone in the popularity of anime as a medium for children.
The four categories are: adaptations of Western stories such as World Masterpiece Theater; adaptations of Japanese media and original works such as Doraemon; works aimed at young girls such as Hello Kitty; and works tied to video game and toy franchises, which have achieved the greatest commercial success.
CoroCoro Comic and Comic BomBom primarily target young boys, especially those in elementary school. Pucchigumi is an example of a children's manga magazine that targets young girls instead.
The annual Shogakukan Manga Award and the Kodansha Manga Award each include a category for children's manga. The Shogakukan Manga Award first added a children's category in 1981.