Yes mumma, I have, two weeks ago.
It's brill. In answer to your Qs. Yes the kids can use the pool and there's a v little children's one too, at all times I think. Spa is separate and you DO need to book in advance (it's for adults).
The hotel is up a steep hill from Polzeath. It's a two minute drive/ten minute walk back down to the fab sweep of Polzeath Bay,a lovely surfing beach with loads of sand for the kids to dig on. I also believe you can walk down a coastal path to the beach from the hotel front.
The restaurant in the hotel is absolutely fine for kids. They have a very nice kid's menu and the staff are SO helpful and welcoming. We didn't feel at all like we shouldn't have the kids there (aged 2 and 4). The chef even showed our two how he was cooking their dinner (the kitchen opens onto the restaurant).
We found the S/C fantastic. There's a Costcutter and Spar at the bottom of the hill (and a General Store practically opp. the hotel). Wadebridge (8 miles away)has a Tesco.
LOADS for kids to do nearby. Crealy Park, beaches, Aquarium, Eden project, local bee keepers etc
Finally the staff can't do enough for you and are so friendly to the children. Despite being a v swanky place it is REALLYkid friendly.
Any other Qs just shout.