Turtle Cove [????- ]
I finally managed to visit this beach, and it looks like a good one to go back to with the family.
The beach is small, but the water was clean and there are lifeguards, a shady area under trees just above the sand, and clean changing rooms. One of the swimmers I spoke to said it gets busy on Sundays and public holidays, but otherwise it is quiet.
We ended up there after for a swim after hiking over from Quarry Bay MTR station. We walked up to Quarry Gap, then down and around the reservoir until we hit Tai Tam Road. From there it's a short walk along the road, and down to the beach. (No pavement / sidewalk for that last section of road though, so be careful). Allow 2 - 3 hours.
Or you can take MTR then bus 14 or 314, or minibus 16M or 16X. Get off at the Turtle Cove stop, which is just after the Redhill Plaza. From the bus stop, walk along to the end of the pavement (you'll be walking away from Redhill Plaza), and you'll see steps leading down on your left. Follow them down to the beach.