I know this will vary from country to country but I grew up in a culture where, as a child, we always put an extra plate on the table if a friend was over. This was true amongst all families regardless of their income background.
If your culture doesn’t do this, is it the assumed understanding that if your child goes to someone’s house, they will be back at your for dinner? I’m assuming the child’s parents are expecting their child to stay for dinner? Are paydays then scheduled around meal times? I’d also love to hear a different perspective on why this is common in another culture!