The Reds are safely into the last eight of the competition thanks to a double by Javier Hernandez and further goals by Phil Jones and Fabio late in the game.
"It was a terrific result," Round told MUTV. "I’m really pleased. To score four at Old Trafford is always special and it’s great to for some of the younger players to be able to experience a game at this level against a good Norwich team.
"I'm very pleased with the performance and very pleased to go through."
Round is convinced that the goals will flow once the champions' luck changes and there were many positives on the night - not least the performances of Wilfried Zaha and Adnan Januzaj.
"We've not quite had the rub of the green in the past few games," he continued. "Hitting the bar and the post a few times. I think that there will be teams on the end of some big scores from us because we’ve got that capability and we’ve got that firepower right the way through the squad.
"I was really pleased for Wilf Zaha to get a start and play so well tonight, a couple of the other younger lads also did well such as Tom Cleverley and, of course, Adnan,