Watch Oom Ferdinand en de toverdrank (1974) Official Trailer

Three children and their uncle find a magic painting in the uncle's attic. When they pronounce a spell, a lady named Esmeralda emerges from the painting. The lady must return to the painting, unless certain conditions are fulfilled. A magic drink, which makes them invisible, should help them. Two thieves (who seem to like nothing but cakes) kidnap one of the children to require a ransom. And it is found that a man, the father of Peter Faber (that's the name of an actor too, but not in this movie) is needed for help. That is not easy, since the they are not on friendly terms with Peter and his father.