Wear one under a wetsuit for comfort, or by itself to keep the sun off. Made of medium weight lycra with flat sewn seams. Sun protection SPF = 50

Kid's chest 23-24 order size: J2
Kid's chest 25-26 order size: J4
Kid's chest 27-28 order size: J6
Kid's chest 29-30 order size: J8
Kid's chest 31-32 order size: J10
Kid's chest 33-34 order size: J12
Kid's chest 35-36 order size: J14

Note: The sizing above is based on a "snug" fit under a wetsuit.
Many parents will order one or two sizes larger for a looser fit when wearing the rashguard alone for sun protection, or to allow more "room to grow".