I have saved the best for last with a real classic that I predict will be read for generations to come just as it was read by my mother when she was a child.
These books were a favorite when it was read to me when I was quite young. They were still favorites when I read them by myself for the first time in elementary school. I still loved them I in middle and high school. The books I made sure to take to college had to include this set. I read them with joy to my children when they were little and even when they were in middle school. I hope that they read them today.
What books could be that important to me? Winnie the Pooh and any of the books by A. A. Milne offer something to people of all ages. The stories are funny and insightful and purely appreciative of the wonders of childhood.
(Please note that I am talking here about the original versions with the original illustrations by Ernest H. Sheperd and not the Disney versions that do not carry the power or the beauty of the original.)
I have memorized bits and pieces of the many poems in these books. It rarely snows that I don't quote Pooh saying
"The more it snows, tiddly pum,
The more it snows, tiddly pum
The more it goes, tiddly pum,
When children ask my age, I almost always recite the classic from Now We Are Six that ends "Now I am six and clever as clever./I think I'll be six forever and ever."
Reading great books helps me feel as youthful as if I were six forever and ever with the added bonus of being allowed to read books from any part of the library and get something from them. Youth and experience all are right there in books.