3-5th grade book - Child Dancing in Front of a Sphere of light

[Matt]

I remember reading a book in the late 80s, in the third to fifth grade (maybe even into middle school) timeframe. I think there were two kids, maybe a brother and sister, and it centered around some kind of mystical ball/sphere of light. I think there was a child dancing in front of the ball on the cover. That’s all I’ve got! Any help would be much appreciated!

[Rainbowheart]

The Moonball?

Charlie from Yonder?

[Rainbowheart]

Still out there, Matt?