And buying that requires knowledge of amazon, knowledge of what phone is useful, knowledge to avoid a scam or faulty product, an email address, a credit card, and a device to order from.

Children are surprisingly clever and have all the time in the world, but they aren't professional pen-testers and don't have the experience needed to use online services before having access to them.

It's far more likely they get a hand-me-down device from a friend and keep it at school, especially if they know such a thing would be confiscated immediately upon discovery. Preventing this interaction would require control over the child's life nearing Amish levels, or prison levels.