My four year-old son is bilingual and he is also learning Mandarin songs and some words in his daycare. Although I have read about the incredible ability of you

My four year-old son is bilingual and he is also learning Mandarin songs and some words in his daycare. Although I have read about the incredible ability of young children to learn up to 5 languages at a time in many linguistics courses, I'm still totally amazed. From my cursory observations, it seems like learning the words is te easy part, the grammar is harder to acquire. Up to perhaps three years old, when he was talking Turkish to us you could easily understand that the underlying grammar was English, he was just filling the slots with different words. Now, he has both grammars fairly down (he's making the cute verb past tense over-generalization mistake, though, i.e. all past tenses are regular with -ed). His language skills seem to be superior to his friends in both languages. This is one data point, of course), but I think learning 2-3 languages at once is beneficial in language development.