The young Gers ran out 4-1 winners at Cappielow Park, earned through a first-half strike from Ross McCausland alongside late goals from 16-year-old Findlay Curtis, James Graham and an Arron Lyall spot-kick.
Speaking to RangersTV after the match, McCallum praised the style of his team throughout a rain-soaked 90 minutes: “I felt we were really aggressive in terms of our out of possession stuff and the way we played through, getting key players in positions between their midfield line was really strong.
“The only bit that was missing in the opening 15 minutes was a second or third goal. The game changes as a result of that, and at half-time it probably feels that 1-1 is quite fair.
“We knew at that point it was a proper game. We spoke about the tactical challenges that we felt caused us problems in the first half. We had a couple of planned substitutions based on where players are returning from injury, which we knew was the case, then we had a couple of enforced injuries like Johnly’s.
“It was a proper game in the second half, it ebbed a little bit and became open, but it was an excellent end to the game clearly. The impact from Findlay Curtis, a young player who has played with the Under-18s, and I’m pleased that we stood up to a difficult game.
“I was pleased that we showed good signs of our identity as a team and individuals over the course of the 90 minutes.
“You look at some of the youngsters on the pitch at the end of the game: 2007-born Chris Eadie and 2006-born Findlay Curtis who have been playing with the Under-18s for the most part.
“I’m really pleased with how the team still tried to show a version of what we want to look like, but we knew it was challenging.”
Scottish Championship side Airdrieonians, managed by former Rangers midfielder Rhys McCabe, await in the next round for the Light Blues.
The clash provides another opportunity for the side to showcase their talent, with McCallum pleased at how his side stood up to the physical challenge which Alloa posed in Greenock.
He continued: “The only way you get to play against a higher quality of opposition is by progressing, so we felt at one point it was going to get to penalty kicks which becomes a lottery.
“The game next will be a tough test. Airdrie are a Championship team who play a good style of football so we’ll look at that when we get to it.
“I’m really pleased that the lads showed who they can be, going into an environment which is a lot different.
“We played against experienced players who have played in the Scottish Premiership at various points, so I’m delighted that the lads showed they can cope and perform in that environment.”