If you are staying in the Hanalei or Princeville area, Anini Beach (southeast of Princeville) is one of the nicest swimmable (and child friendly) beaches on the northern side of Kauai (even during the rough winter season).  For those that want shade, it is also ideal due to the Kamani trees that grow on and near the beach (especially after high noon).  There is plenty of sun if you also are a sun worshipper.  It may not be the best for snorkeling but there are several pockets of coral reef and calm waters for beginners.  There are a couple of restrooms/bathhouses.  The beach is very "walkable" and has some interesting "trees" on the sandy beach making for some interesting photo-ops.

This beach is tricky to drive to. The turnoff is not well marked so you need to be watching the highway milemarkers. Detailed driving directions and safety precautions are outlined in the Kauai Trailblazer guidebook.

There is a dangerous outgoing current that is easy to spot if you know where to look. There's a photo of two people who were rescued from it in the book. Ocean safety staff have mounted rescue equipment within reach at many of Kauai's beaches. Look for the red flotation device on a pole, they're easy to recognize. Heed the motto: "if in doubt, don't go out."