Hi Dianne,
The kayaks and other water toys such as the paddle boats can be checked out at the Dive Center. You do need to leave your room key and show some ID. I would use a copy of my passport. (Let us know if this works but it doesn’t seem reasonable that they would expect guests to carry passports.)
Regarding flip fops, I saw this question asked on another site. The management answered that sandals are allowed. That said, I believe I saw flip flops worn in PC. Dress code was very relaxed there.
I don’t think they allow adults to stay in the kids club. They will give the parent a beeper so they can easily contact you if there’s a problem.
When are you going?