This movie is one of the best ever made, animated or live-action, people or animals. Parts may be scary for your children, but those parts are short-lived and can be easily explained to calm their fears.
The plot is quite simple: A fieldmouse, Mrs. Brisby, must move her family's home before spring plowing, but there's a problem: her son is sick and cannot be moved. Therefore, she calls on the mysterious rats of NIMH (a laboratory), who have been injected with chemicals to increase their intelligence. In the process, she has to face an owl's den, a cat, a bumbling and hilarious crow, and treachery in the ranks of the rats.
The ending is truly magical and very powerful when Mrs. Brisby uses her stone ("which holds great power when used by one of courage") to do what even the rats cannot. A great tale of courage, and how you can do anything if you try.
Bottom line: Well-animated, well-lit, well-told, well-voiced. As good as any movie can get, for adults or children!!!