What’s with all the bad grammar in kids’ books?

I've been consistently impressed by my oldest daughter's vocabulary and grasp of grammar as she gets older (almost 6! where does the time go?). I commented recently to my husband how impressive it is that she corrects her own grammar aloud and he said, "It's because she reads." And she does. The conversation got me thinking. Our kids learn the English language through what they hear spoken around them and from what they read, whether it is read aloud to them or they read on their own.