I’m now having doubts about Palm Springs. We’ll be there in August and it seems like it’ll be too hot to fully enjoy it.
I don’t recall suffering particularly from the heat in Palm Springs. The aviation museum should interest the kids—part of the collection is indoors, so no problem there. And if you take the tram, it’ll be almost cool at the top!
The activities are pretty limited, so you’ll often be in the air-conditioned car between spots or in your hotel room. The rest of the time, you’ll be in the pool (the kids will love it—it can be a relaxing moment for them, worth including), because you’ll definitely have sunshine!
Joshua Tree NP is easy to visit—it’s mostly flat.
In conclusion, I wasn’t bothered *that* much by the high temperatures, even though I was expecting hell!
That said, I went when it was my tenth or fifteenth trip to the U.S., and even though I enjoyed it, I never thought, "Darn, I should’ve come sooner." It’s interesting, but not necessarily a must-see unless you’re a die-hard parks lover—Joshua Tree is still really nice, though.