United started slowly and Vale capitalised with two well taken goals.
But the home team rallied with finishes from Robbie Swinburne and Bobby Skinner to make things all level at the break.
The Valiants reasserted their authority in the second period and two further goals secured their victory.
"It was a very average performance from us," youth boss Mark Birch said. "We had spells in the game but it's a reminder that it takes concentration for the full 90 minutes or you get punished."