Colors of the Rainbow (1980)

A group of children are so impatient to be grown up, that they decide to discover if a folk tale that drinking from the end of a rainbows fountain, will really turn them into adults. To do this, they steal a boat and set out for rainbows end. Things don't go to plan, when they are pulled off course to an uninhabited island, while their parents rush around searching for them. As luck would have it, they're rescued by fishermen and returned home; now understanding the adult world and appreciating childhood a little more.