After realising sonshine boy's mandarin came to a standstill last year, i went on a mad spree searching and purchasing Chinese books. I bought, not 5, not 20 but 80 over books in a breath!
At first i really didn't know how and where to start teaching him. But i realised N picked up a sizable number of English vocabulary just by listening me read aloud to him every night. I have to sidetrack here and share that since N was younger i started a rigorous reading regime with him. I read a set (maybe 10 over books) of English and Chinese books to him at least 3 times a day- in a seating. Sonshine enjoyed it and could sit on my lap for as long as i was willing to read. But alas, my stamina wasn't compatible to his appetite for books! Sad to say, its down to just one time a day (or rather night) now. Every night, we would read at least 7-10 English books in a sitting. Again, the boy would like to read more but i cannot allow it otherwise it would over-run into his bedtime. :(
Anyway, i began my mandarin 'lesson' by reading 5-7 Chinese books every night (on top of the English books). As i had expected it worked like magic! Sonshine's mandarin has improved and he has picked up a number of Chinese words, even learnt to converse in Mandarin (simple ones of course, mummy's mandarin ain't that fantastic either)! Whoo-hoo!