We were a little concerned that the force of the blow and the fact that it took the skin off his stomach (and left it imprinted on the inside of the shirt!) so I drove him over to the hospital after work to have a professional give him a once-over. While we did have an almost 6 hour wait there, they took it seriously enough to do a urine test and ultrasound to ensure that there wasn't any internal injury. Thankfully, it looks like he'll just be tender on his tummy for a bit and have a very odd scar to show to his friends when he's older.
And I have to say, for a kid in some amount of pain and with not a lot to do, Garrett handled the long wait at the hospital like a trooper. He played his DS, my 3DS, my iPhone, read some magazines, flounced about a bit and ate a bunch of junk food from the vending machine with nary a complaint. I think he was more interested in all of the stuff going on through the glass doors into the ward and with all of the people around to realize how dull it was!
To add insult to injury to this whole evening, we got trapped in the parking lot for about 10 minutes when we were trying to leave. On the upside, we didn't have to pay the obscenely high cost for parking ($16 to park for 2 hours? SERIOUSLY?!?) but it was kind of annoying nonetheless.