We've been there twice, not recently though!
When we went we found it to be nice and quiet, I wouldn't say there would be much for an 11 year old to do, apart from exploring the surrounding woodland walks. I don't know how far you would have to travel for a sandy beach, but there is a sea life centre nearby.
If you are going during the summer holidays, then I would strongly advise plenty of insect repellent - the midges are quite bad!!