wow sounds like a crazy story from the 80's to 90's although it sounds "too good" It seems like a mix of Flowers in the Attic and The People Under the Stairs. (Although from my understanding Was Craven was going to make Flowers and the deal broke... which may be the reason why both stories are simular except people is focused with a thrill ride vs Flowers a more drama story.)
Although neither story (as I remember forces the children to live in the shed) so it's quite likely this story your looking for is a rip-off from Flowers/People.
I was looking at possible rip-offs and having no luck in finding such movie.
I did find a movie called Army Brats [Schatjes!] (1984) that may match the movie your talking about, although I have not seen it but from my understanding it's a comedy. The ending of the trailer seemed to match what your looking for.