First of all, a child can acquire the correct pronunciation and intonation of the language. This is difficult to get after one’s puberty.
Secondly, the child can learn independent thinking. Independent thinking, the focus of the western education, is one of the most important quality for one’s future study, career and even his entire life.
Finally, going abroad to study at an early age enables the child to mix himself into the social and cultural life of the target country which helps to form his own identity in the long run.