Re: adoped children

In all likelihood they were culled (removed) from the game as you can not have a household with only children, However you can try @Bubblye suggestion to see if they were merged with another household.

If you have saved the household to your Library before the adults died you can find them there and merge them with another family.

If the adults died from accidents instead of old age you can also load a previous savegame to save the family.