I have travel insurance with Direct Line and I have had to claim on two different trips, first time we went to the states and my infant son had some trouble feeding, he was tongue tied and we had that fixed, we weren't able to go home when we were supposed to and Direct Line paid out for new flights for us. The second time we were in Florida due to go home on a Saturday, on the Thursday my son, who was 13 months old came down with Chicken Pox, so we were unable to fly home. We had to change hotels, extend our rental car, change our flights, and spend money on incidentals (food, medicine, etc) We claimed everything back with Direct Line and they paid out no questions asked.
I don't know who will and who won't cover you, but its worth ringing and asking. I like Direct Line, but again, there are lots of good services out there.