If Korean is your goal, I would advise against using children's books. Korean children learn a rather strange mixture of Korean, coupled with this "child's language" version that uses different vocabulary and onomatopoeia for many adjectives. For example, children will call a dog "멍멍" almost all the time, but the "adult" word for dog is "개" or "강아지" for a puppy. My first Korean teacher bought me a book for 5-year-olds, and she made me quit after a few weeks because she said I was learning to talk like a child.

This is my advice. First, don't ever waste your time learning something you won't use. Learn phrases for things you will be saying a lot, and practice them until it's as easy as breathing. This is how we learn our own languages. Second, to learn grammar, deconstruct the phrases you're learning. They should use pretty basic grammar for daily phrases, so it's a great place to start. Don't rush. People usually rush through basics, and develop big problems later because their "foundation" is weak. Third, songs. I say songs because it's much easier to find lyrics in Korean and English. It's really difficult to find Korean subtitles for most TV shows and dramas (been trying for years to find them). Now, for the stats. Vocabulary. Study ONLY word frequency lists to start with. Using English as an example, if you memorize the 3,000 most common English words, you will be able to understand 95% of all you read and hear. For some languages, like French, the number is even less than 3,000 (600 is the estimate I've found for French). You want to hit that 95% number as quickly as possible because that's the magical number where you become able to learn new words based on context, just like we do in our native languages. So, the short version: 1. Learn phrases you will use. 2. Learn basic grammar by breaking down those phrases. 3. Use songs to learn some more complex grammar and informal speech. 4. Graduate to TV shows if you can find subtitles in the target language. Always, always, always study vocabulary. With the goal of learning the 3,000 most frequent words, learning 5 new words a day will give you 95% understanding in less than 2 years (600 days, approximately).

Also does reading helps ? Reading childrens books ? or will it just improve reading.