Hi Tweetie Pie
I'm not sure if you are already there - or still to go - but, for information, the Mediterranean is not a tidal ocean which means there are no tides. The currents and waves are all created by the action of the wind and shipping.
All Pefkos and Lindos beaches will be perfectly safe to snorkel for your son - and with the crystal clear waters he should have some fantastic views. I personally like Haraki beach (up the coast from Lindos but on the bus route) - but it is pebbles rather than sand so not everyones cup of tea. But if you eat/drink in the beachside cafes then they don't charge for using the sunbeds and shades.
Just one thing to remember along all that stretch of coast - the beaches drop away very quickly so that 20 feet from the shore and you can be out of your depth - it means you don't have to go far to be in swimming depth of water.
If you do go to Lindos I would disagree with Marcuschap and suggest Pallas or Main beaches - but only because there are more cafes and restaurants there, and shops if you realise you've run out of water - and this time of year you will need plenty (we reached 45 degrees during the day at the end of June this year).
If you aren't already there, enjoy your holiday. If you are, then I hope you are enjoying your Holiday.
Say Hello to Christos at the Eclipse Bar for me - and Phillip (the DJ at Pefkos by Night).
Dave