Jeff, if you are new to kayaking, I wouldn't recommend jumping into Class III on the Front Range unless you have a roll and have worked your way up to that level. You will probably lose your boat and bang your head and it may ruin you on Kayaking, which, even though the Buzz is giving you a hard time about calling your boats "yaks", no one here wants.
I would take your boats to do the Deckers run once the water goes down below 600 or so. It may be a while though... Description here:
https://www.americanwhitewater.org/content/River/detail/id/424/
Take your boats to Glenwood Springs and run the Colorado River from Grizzly Creek down to town or South Canyon. If you have a weekend, go to Moab and hit up the Moab Daily section... deeper water and more forgiven than a class III creek on the front range. Glenwood is a nice staging area for beginning kayakers, you can run the Grizzly Creek section and then the Cemetery run on the Roaring Fork if you felt like you handled it well. If that goes well and you start to have some roll experience, a first "class III" could be the Upper Colorado (Pumphouse section)...
If you want a sense for front range "class II" take your boats to Golden and park by lions park and run through the whitewater course through town. Make sure you boat and/or swim to shore before the Coors dam though. In a few more weeks it will be more easy going and a fun place to play around.
I've never run S. Platte through Denver (below Chatfield), but it has some obstacles ... if something looks like a Horizon line, make sure to get out and Scout. Santa Fe Blvd. is a street in Littleton. You may want to look at joining Colorado Whitewater, they have events for people who are starting out.