"Harry Potter" actress EMMA WATSON had in incident at JFK airport in New York City recently, when security mistook her for an UNACCOMPANIED MINOR.

She Tweeted, "Passport control: 'unaccompanied minor?' Me: 'sorry?'  Passport control:  'where is ur guardian?'  Me: 'I'm 22!!!!!!! #neverwearingabackpackagain."

She added, "The really sad thing is that this is not the first time this has happened."  (She does look like a kid, especially with that pixie haircut.)