I've seen other people post about books they read long ago and I've always meant to do the same. There's a series of three or four books I read when I was about 12 or 13 that I really want to remember better, but I'm completely blanking on the name.

It was definitely set in England, in the mid to late 20th century, and the characters were four kids in their tweens or early teens. They were guided by an older man, maybe the grandfather of one or two of the kids. They had some powers associated with special objects (maybe a holy grail of sorts?) It was all connected to an old secret organization that was in a struggle to contain some great evil. I think the kids' powers might have been connected to the elements.

So, does any of this ring a bell, all-knowing Hivemind?