How did your trip went? Well, bringing along kids during travel is quite a challenge that's why I really do understand that you cut your trip and and stay somewhere overnight before proceeding. Quite hassle but better for everybody and most specially for the kids. When we took our trip to Cornwall, we also took a stop at Exeter. I think it's the most ideal place. We stayed at Bluechip's 2 The Square accommodation (check their cottages here:
http://www.bluechipholidays.co.uk/devon-holiday-cottage). Quite affordable and near the road and the beach. We didn't have to rush when we got there. The scenery in Exeter is really amazing. It's nice to take walks there. If anyone comes to take a stop in Exeter next time, I here are some walking trails that you can take before moving on to your trip.
http://www.mapmywalk.com/gb/exeter-eng/