Will Smith and Jada Pinkett Smith took their tight, toned bodies to the beach today in Hawaii -- proving once again ... Jada is the hottest 42-year-old mom in a 2-piece.

Mr. & Mrs. Smith had something for everyone -- her toned ass barely covered in a bikini ... and his ripped arms in a tank top.

If you're impressed -- you're not alone. 13-year-old Willow was there too ... and looked pretty awestruck by her parents' ridiculous physiques.

Will still rules in Summertime.