I think this was a family film made in the eighties, possibly late seventies. It may have even been a Disney film (live action, not animated).
There is a family, or group of people, living in the woods. Between the roots of a big old tree is a spring which turns out to be the fountain of eternal life. All the family members have drunk from it. The water "freezes" the person who drinks it at their current age (in other words, if a child drinks from it, he'll be a child forever). At one point a kid falls from the top of a ferris wheel. Everyone is shocked when he gets up and walks away.
There is also a scene where a guest is offered dinner at the house in the woods, and two old women offer up fancy, mouth-watering meals to the guest while a third old woman offers up beef stew or something similarly bland and mundane.
I saw this movie as a kid but can't figure out what it was! Help much appreciated.