Downey has good public transportation with buses and trains available at convenient locations. If you prefer private transportation, renting a car is the best option. Parking is usually free unless mentioned otherwise. The estimated travel time between the locations is approximately 10-30 minutes depending on the time of day.
If you have extra time, check out the Kandy Kays of California candy factory or hop on over to the neighboring city of Norwalk to visit the Norwalk Arts and Sports Complex. If you have less time, cut out either Rancho Los Amigos or Rancho Los Cerritos, as they are both historical locations. Also, note that some places may close on certain days, so make sure to check their website or call ahead to ensure their availability.