Personally, I am fine with it, since it is becoming much more common, and certainly it is the way people really do speak. But the English teacher part of me still pauses. That said, I currently read many, many picture books to my 15 month old girl-- so I like the idea of being inclusive. I've noticed that many picture books use masculine pronouns, and I wish they didn't. Ack, why can't the English language have a gender neutral singular pronoun!? Would it be possible to alternate? (Not sure how often such phrases come up in your story.)