If the big artery in the neck is pressed too hard, the body may slow the heart and relax blood vessels, which can make the brain get less blood and cause someone to faint for a short time.
Simple, child-friendly explanation for a 7-year-old: pressing the carotid artery can trick the body into slowing the heart and lowering blood flow to the brain, which can cause fainting for a short time.
If the big artery in the neck is pressed too hard, the body may slow the heart and relax blood vessels, which can make the brain get less blood and cause someone to faint for a short time.