This was a lovely little movie made i think in 1971.
it starred Jack Wild and Mark Lester and the soundtrack was by the Bee Gees. I have never forgotten this film. The title acronym S.W.A.L.K stands for "Sealed With A Loving Kiss" and came from the 2nd World War, it's used by courting couple's writing love letters to each other.
It's of it's era, and is about innocent first love. Happy times.