I'm not sure which route your son took, but from the car rental facility, you can take I 15 to Tropicana, left on Tropicana to Polaris, and a right on Polaris to Harmon. If you make a right on Harmon it will bring to to the ramp for Aria/Vdara. You can also get there by going on Frank Sinatra, take the entrance to Monte Carlo, then there is a back way through the garage to get to the main entrance of Aria off LV Blvd, but if you don't know this way, you will get lost.
Larry (limo driver) from Las Vegas