Cam Newton turns 28 today ... and he celebrated by hitting the water with the mother of his children on a crazy expensive Caribbean vacation. 

Cam and Kia Proctor -- who he has 2 kids with -- were spotted out on jet skis Wednesday ... having a blast. 

But the best part ... Cam made his own birthday music video showing off all the awesome stuff he's been doing on vacation ... and it's SICK AS HELL! 

Yachts, ATVs, dance parties ... looks like his birthday wish has already come true.   

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