I think it depends....
DD 2.8 had been recognizing some letters on her own since about 22 months, at 29 months I bought the leap frog letter factory and after one viewing she knew them all, upper and lower case and their sounds and pointed them out everywhere. Many of her toys are educational, we have a good mix, but what she plays with 99 precent of the time would be considered educational, but that is her choice, she is much more in to workbooks, puzzles, mazes, rhyming games, etc then dolls, her play kitchen, etc.
She has been asking how to read for several months...I mean even getting upset when looking at a new book saying "I don't know these words yet" very tearfully. So I have started showing her some site words while reading, which she learned in 2 days and now points out everywhere, plus she had been reading signs and street signs on her own for a while...she even asks to go for walks to read signs. I have started to show her how to sound out words now because she is so eager...if it works great, if not then she will learn when she's ready.
I guess you can't really know unless you are with them 24/7. DD has always been very advanced verbaly and mathmatically, but I would say mainly if I introduce a concept to her, or even mention a new concept, she tends to grasp it immediately....no flash cards, or drilling, just one conversation and she knows it....to me the drilling would be more hothousing, but I also believe no matter what yopu introduce when, if a child is not ready then he or she won't grasp it.
