Orbiting Jupiter question

I recently haven been wanting to re-read this book I read a few years back but completely forgot the name and the author! If any of you can help me...I'll describe it

So this family breaks down on the side of the road, but they get help and are taken in to a town that is later to be found out is magic and not everyone can see or enter it. The main girl and her brother find out the people in this town eat these magic berries that make you see the next day in your dream while your sleeping. The kids mom starts taking them, but when they decide the kids will not take them, they are kicked from the town. This causes side effects from the berries to occur to the mom, like major headaches and fatigue. At the end they make it out alive.

I am so desperate because it was such a good book and it would be so great if any of you knew what I was talking about!!