I am looking for the name of a book I read close to 20 years ago as a child. It’s one of the books that made me fall in love with reading and I’ve never been able to find it. Some of the details may be off as it was so long ago but- a brother and sister somehow end up on a far away island. And while they’re there they realize everyone has great respect for the children and the children are very well spoken and wise. But these people it turns out are born out of caves old, and they grow young as they age. That’s about all I can re-call. Thanks for your help!