Snorkeling off a few piers can be enjoyable like at Ramon's and Caribe Island. For young ones and old ones that have not snorkeled in years, or hey you just want to check you gear, enjoy!
Ramon's has a ladder at the end of their pier for access (ok, it can still be a challenge, but I'm old and overweight). My wife and I snorkeled there several times last trip and saw 100's of fish directly under the pier including 10 or so different species. Also, as Peter Jones has said, the turtle grass can hold small treasures (sea horses). Don't wander far from the pier and keep an "ear" out for boats. I would really like to try at Wet Willies, but a lot of boat traffic.
Hey get wet and see what is there and get ready for Ho Chan, Shark & Sting Ray Alley, Mexico Rocks!