Children learn languages easily
The best age to learn languages is when we are quite young. If from birth, children are around people who speak different languages, then it is quite usual for them to be able to learn, understand and not get confused by up to 6 languages at the same time.
The best way for children to learn foreign languages is the same way they learn their native tongue. They only have to have access on a regular basis with foreign speaking people they will soon learn.
If each person of a different nationality speaks to the child in his or her own language and only that language, then the child will learn. If they hear different languages on a regular basis then they must learn. Young brains are like sponges. They will soak up things and children learn without any effort.
I used to know someone in Germany who was American, her mother and family were German, and her husband was Mexican. Her son would speak German to the grandmother because she could only speak German. His father spoke to him in Spanish and his mother in English. The only problem was that because he knew his father could speak English whenever his father spoke to him he answered in English. If his mother tried to speak to him in German he only answered in English. He understood everything but spoke English more often so this was the language he used. If he saw any of his father’s relatives who couldn’t speak English he would answer in Spanish, which used to upset his father but it wasn’t a deliberate thing on the child’s part. He just spoke in the language which felt comfortable to him at the time.
If you take this as an example, if the person speaking the foreign language never answers in the child’s language then he must answer in that language or be ignored. Children don’t like to be ignored and like to speak. They want to be heard and so will speak. That is how a child coming from another land, suddenly being immersed in a class with other children who do not know his language is generally fluent in the new language in a few months. They don’t need a teacher. It is their natural need to speak which makes them learn.
It is also not useful just to speak a language; if a person cannot read it they do not truly understand it. If you think about reading, the words are in your mind, as an image. Then there is the grammar and syntax which must be learned. If it is not done thoroughly, then it is wasted effort on the most part and it would just be a jumble of sounds in the mind.
If anyone has the luck to be able to learn several languages from birth, then in my opinion it is one of the greatest gifts they can receive.