I decided about a year ago not to jump Hanni (now 4yr1mo) to chapter books, but to keep going with the more complex picture books. Besides the more interesting vocab and sentence structure, there are tons of opportunities for discussing character, motivation, plot structure, irony, humor, culture, history, and even styles of art-work.
I just made an interesting discovery, too. The Egg Tree by Katherine Milhous is in our current rotation, and I noticed how long it is, and how complex (it's got about four mini-plots). A quick web search showed that it's about 2,100 words. "Easy chapter books" may be as short as 4,000!
I'm keeping Hanni on picture books as long as possible. The good ones that keep her stimulated are increasingly scarce as she matures, but definitely worth the hunt. (I would love to make and post a list of the real gems we've found, but I feel a little overwhelmed by that project.)
I've worried too about the mismatch when she starts to read, but I tend to agree with those who are saying that the exposure to literature will help her to make that leap.
