We went to Chateau de Chillon (www.chillon.ch/en) on Wednesday. It is about 45 minutes away when we take the expressway and about 90 when taking the road along the lake (a mistake I will only make once!)
The kids both did fairly well, so we were able to spend about 2 hours wandering around. Pictures will be posted soon. I think we're off to find another castle today, but it is a national holiday and they might all be closed.