Is 100 degrees too hot for a 6 year old?

So I want to preface that we live in an area where it can get pretty hot but 100 degrees is a lot hotter than usual for us so we’re not used to it. My MIL invited us to go swimming this weekend and it’s supposed to be 100 and probably will feel hotter than that. Im sure some of you live in areas where 100+ during the summer is normal and you’re used to it but if you’re not used to that, would that be too hot for a 6 year old?