Liverpool full-back Alexander-Arnold helped the Young Lions seal qualification for the U19 European Championship with a goal in each half.
The 18-year-old Scouser opened the scoring after just nine minutes, then doubled England's advantage with a penalty midway through the second period.
A late third goal from Arsenal forward Chris Willock wrapped up all three points for Keith Downing's side, who have sealed their spot at the U19 Euros with a qualifying game to spare.