2007-born Josh Gentles got the scoring underway in the opening period as he celebrated his first B Team goal by planting a powerful header into the bottom corner, before the young Gers emerged for the second half with a renewed vigour and scored a further three goals without reply through Bailey Rice, James Graham and Tyler Pasnik.
Speaking to RangersTV after the victory, McCallum reflected: "I enjoyed some parts of it, probably the moment Josh Gentles comes on and scores, and then into the second half.
"The first part of the game, it took a little bit too long for the guys to get to a level that they expect from themselves and hold themselves accountable to reach.
"We were a little bit passive without the ball, and arguably we needed to understand how to get better control of the pitch, but they know that and we've played against a similar style of football.
"But it took us too long to get to a point of understanding what we needed to look like when we didn't have the ball and find moments to go and get the ball back at key parts of the pitch, but once we got that, and we spoke about it at half-time, it becomes a willingness to go and actually go after it.
"I thought second half we were much better. I thought Josh [Gentles] coming on, his goal was excellent and sets a tone within the game, before we reset at half-time and I was really pleased with the second half performance."
Although McCallum was delighted at his side's second half performance overall, he was keen to underline the contribution from 16-year-old Gentles who broke the deadlock midway through the first half.
The Welsh Under-17 international met a dangerous delivery from Cole McKinnon and glanced a tremendous header into the bottom corner to initiate the scoring for Rangers.
He continued: "He [Gentles] has just had a round of applause in the dressing room because there are older players in the group, players who have been close to the first-team, and there's a young kid born in 2007 and impacting the game the way he did.
"But it wasn't just his goal; there was a lot more to it. He brought an energy, and he had a pretty clear understanding of what to do.
"I'm really pleased for him. His goal was excellent, but there was a lot more to the game that he's contributed to that's made him deserving of the feeling that he got from the rest of the team."