My XILs have a caravan there so we don't gobut good for kids - XH takes DD there and they love it.
I would say add how long it takes to get to Bromley from Croyden and then add 1.5 to 2 hours just to be on the safe side.
There si a seafood shack on the beach you must visit though - ahve to take own booze but the seafood is lovely. If you see 2 oldies and a younger man who look mean spirited and nasty give them apoke with your fork as probably my XH & ILs!