Orange swim hat from Sun Busters, SPF 50+.  Designed in Australia, this is chlorine resistant too!  

Marked a kids size L - from Amazon this seems to be a 5-6 but check these measurements to be sure - around the edge that sits in contact with the head is about 20" UNstretched. 

Excellent condition with no holes, stains, or signs of wear-n-tear...non-smoking home too.