One of my friends does single parent holidays - sometimes in France but she’s done a glamping one off grid somewhere in the south west and said it was fab. No WiFi so the kids spoke to each other and even to their parents 
. Sounds great Happier and I agree, it’s the little details they remember, not necessarily the Big Bang stuff. So it doesn’t really matter where you are (UK /abroad /whatever). It’s the ice creams and the bickering that they’ll remember 
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Dawlish is lovely Curvy, I’m sure you’ll have a brilliant time. We often go down to Paignton in good weather when in Devon. Nice beach and not too busy. There’s also an amusement park there right by the beach, though I’ve never been. Possibly good for your older ones. Goodrington also has a water park which looks quite fun, again it’s right by the beach. Teignmouth pier (horrible arcade - but then I hate arcades!) has a cool thing at the far end called a ‘black hole’ - it’s a fascinating parabolic surface that you roll coins down (save coppers for it - 2ps are best!) and they sort of roll down in a fascinating circle. DS loves it . My granny lived there until she died last year so we went often, probably won’t go much now, sadly.
There’s also a steam train that goes from Paignton to Kingswear, with a short ferry ride across the harbour to Dartmouth, and that’s really nice - And Dartmouth is a pretty little town to spend a few hours in.
I fancy Devon now but it’s Wales for us this year! We went away for 2 nights over the bank holiday (air bnb in Suffolk) and while we were away we joined English Heritage, because we went to one property that weekend and there’s also loads of EH properties near where we are staying in Wales so it was going to be worth it. We also joined the RSPB because DH said it was a ‘good thing to do’. So that was veeeery expensive but we’re hoping to get some mileage out of them both over the summer!