Sojarr of Titan by Manly Wade Wellman
When the spaceship crashed on Saturn's largest moon, the pilot adventurer died. But his infant son did not. Raising himself in the wilds of an alien world, Sojarr survives, and thrives, discovering a strange tribe of gypsy humans, and battling roving bands of monstrous natives...
Until the day another ship falls from the sky and threatens to throw two worlds into chaos!