If you're going to book a "premium" suite, check out the standard room rates and use the 9k point per night to upgrade into them.
PH is much nicer than the Andaz. Not even in the same league of hotels. I'm not sure that actually translates into a better kid destination though. Have you looked into Ziva as I think it might be more kid centric? (albeit I've never stayed here... just a thought).
The main pools at the PH are not heated for what its worth. The water is somewhat shallow so the sun does a fairly good job at heating it (plus 2-3 G&Ts also help).
Nearly all Caribbean/Mexico Hyatts are offering free COVID tests on departure. You do however have to get tested before arriving to St Kitts on your own dime.