United's U18s were comfortably beaten on their return to league action at the weekend.
Speaking after making 10 changes from the team that started the FA Youth Cup tie against Worcester City, coach Travis Binnion offered no excuses for the defeat:
"It was a poor display, we were second best throughout. We are looking to give everyone an opportunity and utilise the squad, given our schedule, but too many didn't perform anywhere near the high standards we expect.
"Birmingham are a good side, probably the best we've played this season, but we certain contributed to our own downfall."
The Blues dominated from start-to-finish, although the Blades should have taken the lead in the 16th minute, when Fixter headed over from close-range following some excellent interchange play.
Birmingham took the lead in the 19th minute, capitilising on some sloppy defending. United failed to close down a winger and despite having a numerical advantage in the penalty box, an unmarked Blue headed home.
Ten minutes later City doubled their lead, after the Blades easily surrendered position in midfield.
The second-half, following a couple of changes for United, saw a much tighter period, although the hosts still had the better of the chances.
Birmingham rounded off the victory by adding a third with the last kick of the game, Eastwood having no chance of saving a powerfully struck effort from 20 yards.
Blades: Eastwood, Koroma (Paling 64), Kedman, Banton (Waters 45), Cheeseman, Ptak, Heh, Whiteman, Eyre, Fixter (Hutchinson 45), Wright.
Unused: Owen, Calvert-Lewin.