One advantage young children have when they are learning their first language is that they are in what language teachers call an “immersion environment”. Everyone around them is usually speaking the language and so their environment is saturated by it. If you are interested in learning a foreign language, look into programs that offer immersion teaching. One famous example of immersion language training are the Ulpan programs in Israel where people go live on a Kibbutz and combine learning Modern Hebrew with agricultural work. Common experience shows that someone with zero previous experience in a language can do remarkably well in an immersion program that includes some good teaching. It's not uncommon for someone to be able to get around and carry on extended conversations in a new language after just eight weeks in an immersion program. The problem, of course, is that immersion programs can be expensive. But there is no faster way of learning a language.