Unfortunately, there isn't a way to go backwards in time with our games. If you choose "Start Over" you will erase all traces of the family and start completely over, choosing a new person to start a new game with.
Probably the best thing to do is to continue to play that generation with the remaining children, or choose to proceed to the next generation (at which point the living children will be grown and ready to be chosen to inherit the house). To do that, go to the Family screen and press the button that starts a new generation. All game progress will be preserved, and the chosen child will start their own family in the house.
There are some ways to possibly rescue the game if you intervene the moment you notice the problem, but they involve copying files and changing the computer's system clock (which is not really something we recommend).
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Barbara
Unicorn
Last Day of Work