You can certainly get a taxi from the taxi stand right out in front of the pier to take you to baby beach and there will be cabs there to bring you back (you might get a phone number just in case). Baby beach is at the southeast corner of Aruba (away from most of the other tourist and hotel areas of the island). The beach is a big lagoon , sandy bottom that never gets deep. Kind of like a giant salt water pool. There is an opening in the breakwater that allows access to the outside of the seawall and snorkelling along the outer seawall is not bad. It is an especially good beach for non swimmers and kids.
Go to the Malmok area, much, much better snorkeling. Rent a car and you can hit a bunch of stops in that genreal area. Do a Google search : Shore Diving the ABC Islands and you'll find a GREAT website with tons of info on snorkeling spots on Aruba, Curacao and Bonaire. Enjoy!