United conceded after just four minutes at the Melbourne Cricket Ground, with unmarked Christopher Ikonomidis beating Tom Heaton from inside the area.
But Ten Hag's side hit back just before the interval, with Scott McTominay's deflected effort restoring parity. Anthony Martial then notched his second goal of pre-season, following some superb link-up play, to hand United a deserved lead.
Marcus Rashford added a third with just over 10 minutes remaining, after another powerful forward run by defender Eric Bailly. Edmond Lupancu then put through his own net to round off the scoring late on.
Ten Hag said, "It was clear that it was going to be a compact opponent, who started really far back waiting for us, and it was difficult for us to create chances. Also, when we went down in the first minute, the team reacted really good and especially over the right side we created a lot of really good chances before half-time. We then got our reward with the turnaround."
On the performance of his young players, Ten Hag added: "This is why we brought them. I want to make an impression on all the players and they got the chance to show what they are capable of – if they can contribute immediately to Man United or whether or not they need a loan period [and] that could be better. There is also other possibilities, but it is good that United has so many talents. They also need improvement and development."