Went to Frinton-on-Sea this week and it was absolutely gorgeous. No amusement arcade. Not even an ice cream hut on the beach. So no nagging kids all day. You need to take loads of food and drinks though. There is a high street with shops at one end of the beach. We went to the other end near the toilets (resonably clean for a beach). There is also a vast expanse of green behind the beach so you can picnic there and not get sand in your sandwiches !
I agree with Broadstairs, the main beach isn't that big but it's nice and there is also a park nearby. Lots of nice eating places too. Margate has a bigger beach but it's not such a pretty town and a bit rougher round the edges. Ramsgate is pretty good too, again not as pretty as Broadstairs and it's quite a walk from the train station to the beach but it's less crowded there.
Rye - may be nice Aloha but it has no beach !
It did used to be one of the Cinque Ports but the sea went out and left it high and dry several hundred years ago (except for a river it is landlocked)
Tips for Camber Sands - don't go in the first carpark (huge dunes to climb over) but turn next right off the main road and carry on to the end of the road where there is another carpark and direct access to the beach (with a few dunes further on for shelter) and some amenities (cafe, toliets, beach shops etc)
I'm always threatening to have a mumnet meetup at Camber one of these days!!