64-68 (early days) Mystery Cache

Here’s a series of rather easy puzzle caches put out to commemorate the years since February 1964 (for no discernable reason).

If you tackle the caches in chronological order (or reverse chronological order) they should be a relatively straightforward circuit out of Great Chart and back which shouldn’t take more than a couple of hours.

A hint to the cache is in the geochecker, as for the puzzle, the Internet is always helpful.

I don’t really remember much back from the early days. Children aged under five these days go to Play School. When I was of that age Play School was a TV program.

“"Here's a house, here's a door. Windows: J K L M”

You’ll find the cache at N51 08 (M+J) (L-K-J) (K+M)  E00 49 (L+L) (M+K) (M*2)