Descanso Gardens, 1418 Descanso Dr; La Cañada Flintridge; 818.949.4200
This 150-acre park/botanical garden's got kid-friendly running areas, plus the "enchanted railroad": a diesel-powered train one-eighth the size of a legit Amtrak.
Mother's Beach, 4101 Admirality Way; Marina Del Rey
The water at this sand-spot's super calm, so it's a great way to hit the shore -- which your sister will clearly want to do -- without her worrying about her kid being swept away into the sea, as that tends to ruin trips.
THE GUEST: YOUR GRANDPARENTS
Just 'cause they're, like, old, doesn't mean they're, like, boring: hit 'em with some classic LA stops, and you'll jog their memories of Clark Gable/ Greta Garbo/ actually being able to drive at night.
Dan Tana's, 9071 Santa Monica Blvd; West Hollywood; 310.275.9444
An institution since the mid-'60s, this cozy, classic eatery may say "Italian Cuisine" over the door, but you're not here for the pasta. Let's be Frank: the pro tip is still to order the Steak Sinatra.