Louise, One Word of Love (1972)

The young Isabelle escapes from the orphanage and she adopted by two chaps on a caravan. They then meet by chance the posh family of Louise- who runs away with the three adventurers when confronted with the reality of having to marry a Belgian with a large moustache and a bald head. They find a dog. Later Louisa degenerates into a minor moment of sexual hedonism and multiplexing with the two chaps before they are all overwhelmed by the Armageddon that was WWI.