Have leotards got padding over the crotch and nipple area? If not then there's going to be a surprise for all if you go swimming in one.
They are usually made from two different materials and swimsuits usually don't allow for the range of motion needed in gymnastics. Most swimsuits I have had shift just from standing up from a sitting position. I am sure if I did gymnastics in them I would be showing more that I would care to.