Bought these for my 6yo to wear with her rash guard.  Although you could probably wear alone as is, I have her wear bikini bottoms underneath - just personal preference.  There isn't a normal panty liner inside like you normally see with a woman's swim suit.  I love this style and she doesn't complain about them being uncomfortable or too tight (she's on the thinner side of the average 6yo).  As long as they hold up to a summer of swimming i will purchase again.