Newcastle's youngsters fell behind at Oakwell Training Ground through Sam Fielding's header in the early stages of the pre-season friendly before United defender Oisín McEntee inadvertently turned Dani Pinollos' cross into his own net to double the Tykes' lead.
United striker Elias Sørensen halved the deficit with a wonderful finish before half-time but, despite Newcastle's attacking dominance in the second half, conceded in the latter stages through Rosaire Longelo's own goal.
Redfearn told nufc.co.uk: "It was a tough first half. I thought they had a strong team out in the first half with a few first-team players in there, which raises the bar. It was good for us because that's the sort of competitive game that you want in pre-season.
"They got the two goals which, from our point of view, were poor. They were strong and pressed us well. In the second half, we got right on top and I thought we were the better side by a long way but the third goal was a real sucker goal when we were creating chances to win the game.
"It's a good workout for the boys. It's important we got another pre-season game in as we had to rearrange this one quickly. Next Monday, we're into the Reading game with the league season starting.
"There's lots of good things and others to look at. We got on the ball well in the second half and dominated, created chances but the final ball was off, which is something to look at.
"I think we can be brighter in and around the box, deliveries into the box and taking opportunities to finish at times, having extra passes when we could have been shooting.
"The build-up play was totally dominant in the second half but the third goal came against the run of play but those things happen. We went more positive and took the wing-backs off, putting on wingers and went after them."
Newcastle kick off their Premier League 2 division two campaign at Reading on Monday, 12th August, with the Magpies defeating the Royals on penalties last term in their voyage to the division two play-off final, losing to Southampton at St. Mary's Stadium.
While Redfearn is targeting a strong start for the youngsters, the former Leeds United manager is hopeful of more under-23 players breaking into United's senior side, with midfielders Sean and Matty Longstaff both featuring into the first-team squad within the last 12 months.
Redfearn added: "It's always important to get off to a good start. The most important thing is getting these players through. With Matty and Sean getting through, it's a light at the end of the tunnel for these boys, which gives them a lift and it's fantastic for the club. It's all credit to the people and staff who have been working at the Academy.
"We've told the lads you need to learn how to win football matches so that's key as well because that will be important in the progression going through to the first team. Like in any season, you want to compete and do well."
