Arnold Schwarzenegger's Love Child -- Jacked Out in a Speedo ... Just Like Dad

Like father, like son -- Arnold Schwarzenegger's 16-year-old love child is already showing off his genetic superiority in a Speedo ... kicking ass at his high school swim meet this weekend.

Joseph Baena stripped down to his skivvies Sunday to represent his Bakersfield high school swim team -- swimming butterfly no less -- and his mom Mildred was right there on the deck cheering him on.

Joseph's been busy the last couple months -- as we reported, he just got his driver's license in January.