JBlack083108_02_X17.jpgJack Black JBlack083108_14_X17.jpg Jack Black may be one of Hollywood's more, er, rotund stars - but it looks like his son Sammy's decided to help him shed a few pounds!

We caught the Tropic Thunder star horsing around with Sammy in the park while his wife Tanya Haden looked on approvingly. Sammy really gave Jack the runaround, too - seriously, we're exhausted just watching the two of 'em go at it!