Calleta would be ideal for your needs.

Costa Calleta! you cant go wrong.. Try The Barcelo Fuertevetura or the Elba sera ...both right in the middle of everything, but its so quiet you'd never know

Caleta is a lovely resort, not too big and a nice shallow beach, safe for kids. If mobility problems are an issue then I would be careful not to book into any of the apartments up the hill at the back of the resort, although we stayed at the Caleta Dorada up the hill at Easter and it was fantastic but it is quite a trek down to the beach and bars.
I'd say have a look at either of the Barcelo hotels, or if you like cheap and cheerful then the Broncemar Beach gets good reviews.
There is a map of Caleta HERE. All the places towards the upper left on the map are up the hill, the places nearer the beach are mostly flat ground.

thanks everyone, i have a few places to consider now