Hey you want to know something? The best thing about Prince Edward Island is that you are literally minutes from the beach.
Probably the best beach closest to Charlottetown is Brackley Beach - about 10-15 minutes from Charlottetown. And just remember, this is a national park, so you have to pay. I always get a summer pass.
Most people don't know, but there is a beach in Stratford - 5 minutes from Charlottetown. It's actually at Tea Hill Provincial Park. Now here's the skinny on it. Not a lot of beach - somewhere to lay and gets some sun, but the water is bathwater warm, and when it's low tide, you can walk for like a kilometer out to see the view - our kids love it, 'cause the water never goes over their heads.
I love Blooming Point beach. It's about 20 minutes from Charlottetown, or you could go to Tracadie Beach. Now with Tracadie Beach, it is a very young crowd, and if you are taking kids, Blooming Point may be a better family destination.
Also 30 minutes from town, is our family's fav beach - Lakeside Beach. Right beside Crowbush golf course. It's a little more private, but has great white sands and is a great spot.
But one of the most fun beaches on the Island is Basin Head in the eastern end of PEI. This is a spot where you can enjoy an awesome beach, great swimming and you can jump off the peir into the water - one of my all- time favorite things to do. Only downside, it's about 1 hour and 15 minutes from Charlottetown.
I hope this helps - really every beach has sand and water, so they're all good hahaha.