Just 40 minutes from Faro Airport
You can catch the little ferry from the river in Tavira town centre which takes you through the lagoon past the flamingos fishing over to the island. It's a lovely relaxing little trip with the sun and sea breeze on your face, you feel like you're blowing all of your troubles away, and it's inexpensive too. You can also take a water taxi there, and if there are a few of you, it's not much dearer either.
When you hop off the ferry you can either stay the lagoon side where the water is still and shallow (perfect for very small children or non swimmers and for snorkelers it's great too.) and the beach is fairly empty, or take a walk through the trees past the half dozen or so restaurants and cocktail bars out to the Atlantic side of the island...
The Island has a real lazy bohemian feel about it, and the beach itself has everything, you can see straight away why the Lonely Planet Guide said it is one of the best 10 beaches in the world for families...11km of clean, golden, blue flag beach gives you plenty of room for peace and quiet and long barefooted walks,... and there's a Naturist section if you want to get totally brown!
Football pitches with goals and nets, volleyball pitches, a stage where you will sometimes get bands playing. Then there's the pier where you can sea fish, or if you are lucky, WATCH THE DOLPHINS PLAYING out at sea.
Then with Pedal boats, bannana and other pull along rides and a couple of bars right on the beach front i don't think you will be bored for a minute!
You don't need to carry loads of stuff with you either, as you can hire sun loungers with or without shades, get cold drinks from the couple of bars that are directly on the beach, then have lunch in one of the restaurants where you can get light snacks or a larger fresh seafood meal, and what better way to round off the day than a long cold cocktail at the sunshine bar on the walk back to the ferry.
If the ferry is not your thing, you can also take a mini train, at the other end of the Island , Barril Beach, though the drive there is quite a bit longer it's worth the trip, there are some lovely beach side restaurants serving great long lunches. It is also a nice walk by the side of the railway lines to the beach through the dunes and over the lagoon.