Thank you for your reply to my comments.
I was familiar with The Door in the Wall. It was one of a large number of HG Wells short stories read to me as a child by my Mother, who grew bored with children’s literature more quickly than I did. Even as a child, the story made me feel a nostalgia for yet earlier childhood, the sort of feeling conjured up by Lewis Carroll when Alice is looking at beautiful garden she cannot (yet) get into.
The Crystal Garden also called to mind an old Tom Stoppard radio play (Where Are They Now, it may have been called) about a school reunion in which one character recalls being perfectly happy on one occasion during childhood. This occasion is not a Christmas morning or birthday, just a walk down a corridor at school during which the boy felt entirely carefree. He says he has never been truly happy since. I wonder if we all have such moments? I hope so. But I also suspect that making shrines of such moments has its dangers.