It may seem obvious that a child in an English-speaking home should be targeting English. But for the child this is not obvious at all. The most that a child can know is that what he or she is hearing is one instance of human language. Working out which one is a task which he or she has to manage alone. English happens to have more speech sounds than most languages. And they combine in more complicated ways than they do in most languages. But the speech sounds themselves are mostly quite simple. Other languages are different in all of these respects.