Flatlander_obsessed_with_c

I've never done any ice climbing but have lots of backpacking and long-distance hiking experience over rough terrain. I was thinking about climbing the DC route up Rainier next summer with RMI, but was wondering how much exposure there is on the route, because my son (who also has lots of experience and is in very good physical shape) has a fear of heights. We've done Whitney in California the Grand Canyon down to Phantom Ranch with no major problems...how much more exposure is there on the DC route of Rainier versus these hikes?