Cameron Diaz and Alex Rodriguez's roller coaster romance is definitely at a high point!

The couple hit Busch Gardens amusement park in Tampa, Florida last Saturday March 13 -- and Diaz, 38, looked every bit an aspiring stepmother, breezily holding hands with the Yankee slugger's daughters Natasha, 6, and Ella, 2.

Diaz has been bonding with Rodriguez's girls (their mom is his ex-wife Cynthia, whom he divorced in 2008) for a while now; back in December, she was photographed holding little Ella in her arms during a trip to Mexico.

Diaz and Rodriguez, 35, rekindled their on-and-off romance last November.