<PERSON>'s daughter, Royalty, was treated to every 3-year-old's birthday dream ... an epic pool party, plus a trip to Six Flags. <PERSON> posted a bunch of pics of Royalty's birthday weekend -- which included what looks like a kid-filled poolside bash, and a day at Bugs Bunny World at Magic Mountain. <PERSON> was front and center during the toddler turn up ... showing everyone his #1 dad side.