By Edward Eager.
I'd better write something about this right now, or I'll never get to it.
First off: I wish I hadn't read the back cover before starting this. You find out what's going on so quickly anyway that I think it would have been more fun to guess it.
This is quite a fun story overall: four siblings find something magic, and growth results. I laughed at quite a few things that I'm sure I would have missed when I was younger. (I don't remember reading this at all before so I probably didn't. But then again, I remember reading Nesbit even though I can no longer recall anything that happened.) The prose isn't flowery but it gets the job done quite well enough.
The one really jarring note was when the children felt it would be somehow wrong to do magic on Sunday, and proceeded to play the rest of the day. No mention was made of church, or the Lord's day, or even a day of rest. Did they intuit some moral subconsciously? I'm having a hard time thinking of other reasons it could have been wrong.
Overall, this was quite a clever, if light, read.