I've gone with the "wait until they are ready" approach as well, DS was 3 years and 2 months when he trained, we have tried training DD1 because she is fine with wees but still poos in undies, so she is back in nappies now. She's 4 next month. Hopefully one day it will just click in her head.

DD2 isn't much younger than yours - she will be 3 in November, she wears undies around the house of her own choosing, and grabs a nappy for wees and poos. We're just letting her lead rather than ask her every hour - and then clean up accidents, seems like a lot of work to me.. and I hate pee on the carpet LOL