The token is only valid for a day after use, so loss and transfer isn't much of an issue.

If A is buying the ticket and immediately transfers it to B, you could end up defeating the aspect-validation element of this system. That mechanism would be strongly analogous to a straw purchase for alcohol or firearms:

<https://en.wikipedia.org/wiki/Straw_purchase>

The likelihood of a large black market for underage Internet access developing is probably low, but informal small-scale attacks would likely be possible, and perhaps attractive to those who could negotiate the transaction on others' behalf.

That said, the underlying mechanism you describe is a good one, and the objections raised so far here largely specious.