35 years ago, whilst at school, my class read a book about a group of children who go through a cave system. Thats all i can remember!!!! The book cover had a picture of a tree by a cave entrance. Anyone take a guess at the title (i'm sure it had the word "tree" in it)
Might it have been Stig of the Dump by Clive King? It was written in 1963 and would have been popular in schools at that time. I'm assuming you were primary age, of course. I seem to remember some children travelled through caves and back in time to help build Stonehenge with their friend Stig, who was a caveman.