Toddler Shark Rashguard

I purchased this Rashguard and bathing shorts for 3 1/2 yr old grandson. I think it’s perfect size, the 5 T and will protect him from the sun while having fun at camp.

We took our 2 1/2 year old to the pool for the first time this summer and used this rash guard and a UPF 50+ pair of trunks as well. We covered all of the uncovered sections of skin in SPF 50+ sunscreen. When we got him home after a couple hours his arms were RED RED RED. He got COOKED. Is this because the "sun-blocking" UPF only works for so long...? He wasn't burnt on his tummy and back. We are all very fair skinned so my husband and I both also wear UPF 50+ rash guards as well, and we didn't get burnt at all. This is my first time using a Carter's brand rash guard, and will probably be my last. The idea behind rash guards is not only extra sun protection, but I also thought (foolishly, it seems) that one can wear them so one DOESN'T have to constantly lather with sunscreen because those areas are protected. Am I being ridiculous or have I been sold a fake "bill of goods?" His Carter's UPF 50+ swimming trunks protected him. I am disappointed and my poor baby is a lil boiled lobster. 🥺