If your kids are swimming in indoor pools a lot, you need chlorine resistant ones if you want them to last. They will cost more (under $50 on sale) but they last and last. It's a different type of fabric and seems to "give" more as they grow. I buy a size up and seem to get 2+ years from a suit. Even then, they are still in good condition. Bought an all-in-one for DD when she was 1.5 and she wore it for 2 years. DS would be in it now if it wasn't bright pink!
Check the labels of the brand names, but I found that the Billabongs etc.. weren't chlorine resistant. Check out this
site, just search for "chlorine resistant" and then you can narrow down by size etc. It will say chlorine resistant in the item description.