It makes me sad, especially when I look at my children. I wonder if they're going to be one of those kids that yearn to leave those stuffed animals behind them without a backwards glance, or if they will suffer from Peter Pan syndrome and never want to grow up.
However, it is something important to think about. Especially if you want children and teens to enjoy your books. Think carefully about the age group you are writing for and write for them. Know your audience. Research the trends and the kid/teen speak. Study how children/teens interact with one another. Any other ideas?
If you know your audience, you can create the type of characters your audience will relate to. Now you've got to work on your story...
Out of curiosity, I put together a poll to see what people think about whether kids are growing too fast. Go and vote!