We have
abroad hot holidays we’ve been to Italy when our 3rd was just turned 6 months, France when our 2nd was 6 months and Portugal when our eldest was just under 1. We also go and visit my in laws each summer and compared to where we live, it’s HOT and so sunny there! We’ve never found it an issue, tbh, but then I hate the heat anyway so I would seek the shade out myself. We’ve stayed in a house with a pool before and just made sure we chose one with a gated pool as she was just starting to walk.
I can honestly say I’ve never not enjoyed a holiday with kids because of the heat/sun
I’ve always seen people say why bother, they won’t remember, it’s so much hassle. And yes, they won’t remember, but we will! And if we just didn’t do anything because they won’t remember we’d never go out til they were about 6
ETA: we usually go on holiday at Easter time because a) it’s cheaper! b) it’s not as hot in other countries. So you can choose when you go to avoid the worst of the heat. That said we did go to France in May, and it was grand.