My friend keeps bringing her bottomless-pit son to our get-togethers

Three couples in our group meet up once every two months. We rotate between hosting at home and eating out, and we pay for everything using our group dues. Our kids are all in high school or college. Whenever we meet at someone's house, one friend always brings her high school son along. Her excuses are always 'I didn't have time to make him dinner' or 'He needs to eat before heading to cram school.' He's been a massive eater since he was a kid—he's tall and weighs almost 100kg. The problem is, this kid is a literal human vacuum. While us adults are just chatting and picking at the food, the dishes disappear in the blink of an eye. On days he doesn't come, 3 or 4 delivery items are plenty, but when he shows up, we have to order double that. And even then, we still run out sometimes... I mean, it's great that he has a healthy appetite, but since the money comes out of our shared dues, I feel like that couple should pitch in more. It feels so petty to bring up food, so I haven't said anything... If it were just a few times, I'd just think 'Oh, he eats well,' but he's come nearly 10 times now and just clears the table. Even with the shared dues, the financial burden is getting ridiculous.