The advantages of learning additional languages early before children reach puberty are that children learn to pronounce and speak more fluently and are not self-conscious about how they sound or if their grammar is perfect. Also language learning is always cultural learning, and with the current globalization trends, these skills are becoming in demand even more.
Children who have the opportunity to pick up a second language while they are still young appear to use the same language-learning strategies throughout life when learning other languages.