Those of you who read/watched "Five Children and It.."?

Question

What are megatherium, ichthyosaurus, and plesioaurus?
What happens to the gold pieces the children get from the fairy?
What does Robert do to the baker's son?
How does Lamb change? How does he get into the house?
Who makes he last wish, and what is it?

Answer 1

Ichthysosaurus and plesiosaurus are dinosaurs, or fossils of said dinosaurs.

The rest can be answered by reading the book.