The same as babies in any country/language. They start off with speaking, their parents and family encourage them and correct them all the time. Then as they get older they start to associate words with collections of letters. My children are bilingual, they have been brought up with 2 languages in the manner above and are fluent in both! Unfortunately when we get older, we do not see being corrected all the time as a good thing and we are afraid of making many mistakes all the time. We believe that adults will not see adults in the same way they see their children. Hope this helps Bob

It is the same with babies all around the world. They start with certain sounds, then murmuring and muttering some syllables, joining them, and uttering the first short words. Then they create short ( usually ungrammatical) sentences, parents correct them several times until they adopt a proper phrase or hort clause. So, it is the same with the babies and the adults - repeating, practicing, using the language freely in a positive and supportive atmosphere, and one begins to master his native language, and the L2 as well. All the best!

I wonder how native english speaking children learn to write and speak their language.

like you and other babys

This is comes naturally to their mother tongue no wonder.