Places like The Big Sheep near Bideford and The Milky Way (a bit further out) are good fun for kiddies.
They have soft play areas and also they can stroke and feed the sheep, watch the ducks being rounded up by a sheep-dog etc. etc.
There's a small play park in Braunton, although your dd may be a bit young (??!!)for it...I'm not sure....not very good at ages and sizes!!
Also...if it's horrid weather you could always go to the leisure centre in Barnstaple for a swim so take your bathers!!!!
HTH.