You hit your friend’s son with a baseball. How do you apologize?

“I was playing catch with friend’s 7 year old son. I looked him right in the eye as I tossed the ball to him, but he didn’t move and the baseball hit him right in the mouth. He bled a little bit, but thankfully he didn’t lose any teeth. Now his parents refuse to talk to me.
Do I owe them an apology, or is it not my fault because he didn’t even move his arm?”