"If a child comes to me and says they've forgotten their lunchbox"
Yes, that's all very well and you're clearly fabulous, but this child DID NOT TELL ANYONE they'd forgotten their lunchbox!!
All these posters saying they can't imagine how on earth no one noticed this child wasn't eating are showing a spectacular lack of imagination. It entirely depends on the school's arrangements for lunch. In my school, children are out playing until their class is called in for lunch. With 240+ children on the playground (apart from those already inside eating), it would be entirely possible for a child to duck out from lining up with their class when called.
I'm afraid I'm wondering if there are some issues with the child if they didn't feel able to inform someone they had no lunch. Of COURSE no school would see any child go hungry IF THEY KNEW ABOUT IT. But at 8 years old in this case, the child has a responsibility to speak up or take the consequences.
Also, I will inform parents on here whose children sign up to school meals, that many, many of them actually don't eat them. Every day, I see countless children swipe almost their entire meal away into the pig bin. They have asked to leave the table, and it's been suggested they try a little more of what's on their plate first, but ultimately no one can force a child to eat. So, many of them don't. And parents don't have a clue, and may well only give a light tea on account of them having had a "proper" lunch.