The book was titled PLANETS, or THE PLANETS. It was written by a man before 1950. I believe his first name may have been George. The story I am most interested in is about two astronauts that crash on the moon and then end up living on an island in the center of a lake inside the moon.
While not a perfect match, this sounds a lot like the novel "Kidnappers of Space" released in the U.S. as "Space Captives of the Golden Men" by M.E. Patchett in 1953. The author is not George and the title doesn't have planet in it. But, it is about the right time period. Too, the boys/astronauts do crash into the moon and live on an island in the middle of a lake under the moon's surface with the Troglodyte like species living there. You might remember the monster called a "Wormisaur" from the lake.
A description of the book is listed at the following site:
True First Edition. From copyright page: "First Published 1953" The book's boards are moderately worn, the endpapers and edges of the pages are foxed, otherwise free of inscription, tightly bound and in very good condition. (VG/No Jacket.) 208pp. This is written under the intials M.E, obviously the old fashioned notion that a female author does not appeal to boys. It lists Ajax and the Drovers under author's other books. A scarce title indeed, a wonderfully unusual copy of her work. The year was 1976 and the great new rocket desgined to carry the first men to the Moon, would soon be launched. But Jim and Bob Steel, sons of the Interplanetary Society in charge of the project, were destined to visit the Moon before the rocket ! They were kidnapped by the golden men of Mars, crash landed on the Moon, and were the first humans to explore its mysteries. They were the happy race of little troglodytes, discovered the horrible wraith-like ''Zombies'', and came face to face with the Wormisaur. This thrilling story is not just a fantasy. The rocket lore, the interplanetary flavour of the book, and the astronautical information are as accurate as present knowledge allows. M. E. Patchett is well-known for imaginative and vivid writing and this exciting book is one of the author's best. Here is a story which all readers will enjoy for it gives a glimpse into the future - perhaps their future as explorers of the Moon. Bookseller Inventory # 1086