I've canceled several trips, mostly September trips at high elevation in which snow was forecast, only to find out that the weather, although cold, was otherwise just fine. I've been on other trips in which the weather forecast was just fine but during the trip all h*** broke loose. There was one particular trip in Oregon's Wallowa Mountains in which it started pouring rain (cloudburst-type), poured all night, and we woke up the next morning to flooded conditions and several inches of snow. Our campsite had turned into a lake (that's how I learned that a wet synthetic bag is no warmer than a wet down bag, as well as making sure the tent site is not in a depression that will turn into a lake with heavy rain) and we had to bail out. On the way down, we found that the creek (fortunately bridged) we had to cross had grown from a little rivulet to a raging torrent, just a few inches below the log bridge we had to cross.
The main thing is to be prepared for such conditions and know how to keep yourself warm and dry when they hit. Weather forecasting is definitely an inexact science! It's mostly based on probability, which (as you know if you've studied probability and statistics) is similar to rolling dice (a favorite textbook problem in that field).
In the Rockies, in particular, you need to be prepared for daily afternoon thunderstorms. This involves not only having good rain gear and a good tent, but also getting down off high, exposed places before the storms hit. Always be concerned about lightning hazards!
The dayhike idea sounds like a good idea for learning to cope with such conditions. So is car-camping in less-than-optimum conditions. Take games to play in the tent with your son! Maybe take a lightweight tarp you can use to cover a cooking-eating area so you're not stuck in the tent the whole time.