I live in Devon and feel sorry for the holiday makers. Yes there are attractions but if you've been expecting days on the beach with a picnic then going to attractions every day is going to make it a very expensive week. For example Paignton zoo is offering free tickets for children with an adult but for two adults it is almost £50 and you will mostly be walking round in the rain.
Plymouth Aquarium is about £70 for two adults and two children, can be more or less depending on times and age of children. At least it is all indoors but it isn't something that will keep you occupied all day.
Kents Cavern in Torquay is again around £50 for a family of 4, the tour lasts an hour but you can probably spin it out to 2 hrs or 2.5 hrs.
Woodlands is a great day out, again round the £70 mark for 2 adults and 2 children unless they are very little but you need a dry day as it is mostly outdoors and going on a wet day you'd miss so much.
If children don't travel by train very often that can be a novelty. A train for 4 of you from Exmouth to say Teignmouth would be about £20 and is about an hour each way, I think you can break your journey and if you get off at Exeter Central you are a short walk to the museum and if by any chance it is dry the park on the front at Teignmouth is good and it is also free.
Yes there's lots to do but it does add up and looking at families trailing round at the moment I don't think lots can afford 2 or 3 attractions a day.
So my sympathies are with families down here at the moment. OP there is lots to do but I hope you weren't hoping for a cheap week.