Arnold's Love Child BOARD STIFF

0816_joseph_baena_beach_launch_EXArnold Schwarzenegger's love child Joseph Baena hit the Malibu surf for some boogie boarding ... less than a month after Arnold's other 13-year-old son Christopher seriously injured himself doing the same thing.

Interesting fact: these pics were snapped over the weekend ... less than a mile away from Christopher's crash. Joseph's day at the beach was injury-free.