grandmother with 2 kids going cross country

I saw this movie on TV in the late 1980s so it had to be the 1980s or earlier. So this grandmother said to her grandchildren (one teenage girl and the boy was younger) “We’re moving to California.” When one of them asked about school, she said, “I’ve already spoken with the principal.” On the way there, the grandmother was overwhelmed driving. When the granddaughter offered to drive, she said “I’m a tough old merch.” The grandmother died shortly after and the grand-daughter continued to drive. Later they got pulled over, and the cop looked at their license plate and said” Where you headed?” Does this sound familiar?

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