I was looking to get a swim diaper that I could wash and re-use instead of continually buying disposable swim diapers.  I bought the 2XL for my 2 year old that is just over 30 lbs.  They were too tight!  She wore them a couple of times and then started complaining that it was too tight and so I was forced back into disposable swim diapers for the rest of our trip.  I should have ordered these earlier so that I could have returned them for a different size.  However, they look great and seem to work well at containing messes as they are snug fitting around the waist and legs.  So, provided you get the right size, I think these are a great pick for a swim diaper.