Hi Sarah.
First off we hope your trip is a pleasant one
I assume that ents district downtown means the entertainment district?
If that is the case have a look at Yaletown Currency Exchange ( GCVY64 ) it will give you a good centre point to find nearby caches. It is just about the only large cache in the downtown area, but can be hard to retrieve at most times (lots of muggles), almost all of the other downtown caches are micros.
There are several caches in the area and at the southern edge of the downtown peninsula is False Creek. Along the southern shore there are several caches and it is a pleasant walk along our very popular seawall.
As a bonus your son will get to ride on our little shuttle ferries which are about 4 metres long and scurry back and forth all over False Creek. Of course if your son is into toys a visit to Granville Island will be a must as they have a great kids mini mall there
West of False Creek is Kitsilano Beach which has a few caches nearby, again a nice walk along the seawall.
As for Airlines to Edmonton & Calgary I think most people would recommend Westjet .
Good luck & have fun!
Chris