Hi there
I'm a Canadian expat living in Paris since 2009. A few thoughts:
Honfleur is very charming but owing to that and its proximity to Paris it will be heaving with people in the summer. It will also be very expensive. This part of Normandy is known as the 21st arrondissement - an extension of posh western Paris.
I'd be more inclined to spend more time in Bayeaux or Dinan area and perhaps go into the Contentin pennisula and explore the white-sand beaches of the bay (not the Channel coast side).
For Brittany, I would recommend an overnight in Mont Saint Michel since you'll already be in the area. In the day it's overrun with tour groups, but they disappear at 5 pm. It really does seem magical at night and first thing in the morning.
5 days in Quimper seems like a lot. Quimper is pretty dull but the surrounding countryside is lovely: the area around Douarnenez Bay is less touristed than other parts of the Brittany coast (exception: the Crozon Pennisula, which is a bit like Yosemite or Yellowstone in the summer). I'd be more inclined to stay in much more charming Pont Croix or better yet on the coast if you can still find available accommodation.
Vannes, a bit like Honfleur, will be overrun. I was just there during the fall school vacation last year, and even in November it felt like half of Paris (including ourselves) were there. Cannot imagine it in the summer. What makes things especially awkward is all the bottlenecks if you want to go to the coast, as it's on a delta with lots of little islands and peninsulas that limit road access.
I'd say skip Vannes and spend those extra 2 days either in Dinan area or Dordogne which both seem more fun travelling with kids.
I've never been to Clermont Ferrand, but I've been meaning to visit the nearby Auvergne in the summer as everyone who's vacationed there tells me that's when an otherwise remote region comes to life without being overrun (notice a theme here?) with gorgeous scenery and villages.
One thing I've noticed is that in in the summer, rural areas will offer some kid-pleasing easy-access outdoor activities - the sort of thing you can do for a few hours, rather than a several day expedition that can be the norm in N. America. For example, river kayaking with a bus shuttle, or renting paddle boats or canoes (btw, the French reverse the terms for Kayak and Canoe). They will cater to French families, so quite likely won't speak English. Something to keep in eye out for when in a popular family vacation spot.
