Batter hits and runs to third then first? I called him out?

So im a 16 year old umpire, umpiring for 5-6u tball. I know what everyones gonn say they are little kids blah blah, but seriously you gotta draw the line somewhere because of the crazy-*** dads and fans...So kid hits the ball runs and touches third base, then runs across the pitcher mound to 1st base, I call him out of the baseline or basepath stating that the runner must run to 1st base. The coach freaked out and its been a year and he still gives me trouble about it. Whats the right call??