can anyone recommend where they bought or what kind of swim cap they use for their toddler

i enrolled my dds in swim lessons, and it says hair longer than 4 inches, child must wear a swim cap, my dd's are two and i don't think they will keep it on, but i want to be prepared with one in case they force the issue

i saw this in one step ahead catalog, but it says more for sun, don't know if this would be good
can't post pic here is the link

http://www.onestepahead.com/catalog/product.jsp?productId=538255&parentCategoryId=100180&categoryId=100182&subCategoryId=117688