Somewhere cheapish and fun for Feb half term, family of five!

[Asalways]

I've looked at the canaries but it looks very expensive - 4k for the week! Any advice welcome!

Unfortunately cheap and school holidays don't exist in the same sentence. If you want sun in February the Canaries is your nearest best bet. Even then it won't be warm enough for pool and sea unless the pool is heated.

Center parcs?
Only the canaries are warm in Europe at that time

Yes to what Lonicera says.
Is sunshine a requirement? If so the Canaries will be the nearest cheapest sunshine holiday. School holiday prices will affect wherever you choose to go.

Innsbruck would be a good call. You can fly to Munich to save money and then drive down. It's beautiful and most hotel arrange day trips the mountains if you fancy a bit of skiing.