I think the archaeological finds at Sutton Hoo inspired this movie. Kit Terrington and Jacqueline Cox visit their uncle, who is digging up a Saxon ship in the woods. Meanwhile, their father's engineer is working with a pal of his to steal a gold cup, which they have lifted from a local museum and buried inadvertently right by the ship. While doing so, they dropped some matches, so there's also a forest fire to contend with.
These Children Film Foundation efforts were produced because the people who backed them thought the American children films that dominated the Saturday matinees were too nasty. Unfortunately, while the camera-work always seems to have been good and a few of the stories well told, most, like like this one, seem more interested in making sure there is nothing to offend anyone, than in making sure there is anything to entertain anyone.
Thus, all the principals -- children and villains -- start as as smug and self-centered. True, the children learn, but there's nothing to make you take an interest in what's going on for the first twenty minutes. In Keaton's THE NAVIGATOR, Buster starts out as a smug fellow we want to kick, and indeed, the movie kicks him a lot as he grows. However, the gags that surround him, even at the beginning, command our attention. Here it's kids being whiny and lazy and mean to each other. Ho hum.
Likewise the villains. At least they get to take a few pratfalls; yet those are taken in such a perfunctory, unornamented and unfeeling way, that they have no impact, neither comic nor telling, even for the characters.
Clearly the people who supervised this had More Important Things in Mind. It's Educational! It warns children to be responsible about matches! I suppose these things are important. However, when it comes to a kiddie matinée movie, first entertain me. Come to think of it, that's still my rule in my seventh decade.