What could it be in The Secret Door in the house of The Family Tree?

Two curious boys surely would love to see. Soon they are wisked back to the magical land, why did they turn that key. Oh my where could they be?

The magical land

The ground sparkled like a million fire flies landed to take a rest. The air smelled sweet like watermellon on a summer's day. Vines of jewels and trees with the golden nuggets dot the land.

Back to the magical land

We''re back, back to the magical land. What sacrifice will they make or lessons to learn when they see the blue moon.