I am a 5 a week 9-5’er but live in Exeter. The one thing Exeter seems to lack for children is a good indoor play area, having said that Dinkies in town would be perfect for your little one and the food is good and reasonably priced. My wife takes our little one to Bear feet in Newton Abbott and says that it’s very good and well worth a visit. I’m not sure where your based but the Waie Inn near Crediton is also excellent for kids with indoor/outdoor play areas and swimming pool, it’s also very reasonably priced. We also have annual membership to Crealey, its a little expensive at £55 (I think) but your youngest would be free and it can be spread out with monthly DD payments, there is loads for the kids to do and even if the weather is grotty there are all the animals inside and a couple of big indoor play areas that are great even for the biggest kid.
Best wishes to you and your family.
P.s. Love the idea of devondadbike – any excuse to get out riding!