I think the language learning ability of kids is really powerful. My daughter is nearly 3 years old. Her mother tongue is cantonese, so her cantonese is just like an adult. She can also communicate in simple English sentences. I think it is normal.
But I am surprised at her reading skill. I bought a set of readers with CD and DVD to her some months ago. There are totally more than 10 books, and she has many other things to play. So I guess she listens to each book for not more than 10 times. Yesterday I suddenly found that she could open the book, point to the sentences one by one and read the whole book to me! There are totally 10 pages and 20 sentences in different sentence structure!
By the way, I think I should clarify that there are more than 10 books in the set (each book with around 10 pages), and my daughter is NOT able to read them ALL. I just choose one that looks easier and interesting for her and she can read it. I have not tried all of these.
Wish to clarify that it actually very depends on whether your kids are interested. (I don't aim to "promote" the book set actually. I believe other book sets by other publishers may also have same effect.)
My girl with mother-tongue is Cantonese, but we train her to speak English starts from new born to age 1.5, then we add in Cantonese more and more until now. We sent her to learn Putonghua during age 2, so she can now handle 3 languages together without mixing up. I think "No TV" is my strategy, but just little bit "Phonics", "Mickey Mouse" programmes when she is infant. (around max 1 hr/ day).
She can even speak out 3-4 首唐詩 when she is only age 2.5.