Milner was influential for England and he drilled in a low drive from 25 yards for the second, before Theo Walcott sealed the win with a delightful clipped finish.
Scunthorpe's Morris replaced Quinn with seven minutes to go.
England U21: Hart, Gardner, Wheater, Taylor, Mattock, Lennon, Noble (Surman 85), Muamba, Huddlestone (Jerome 79), Milner, Walcott (Johnson 85).
Subs Not Used: Lewis, Mancienne, Moore, O'Hara.
Booked: Wheater, Johnson.
Goals: O'Halloran 60 og, Milner 68, Walcott 78.
Rep of Ireland U21: Randolph, Nolan, O'Cearuill, O'Dea, O'Halloran, O'Toole, Garvan, Quinn (Morris 83), Stokes (O'Brien 87), Clarke (Rooney 65), Andrew Keogh.
Subs Not Used: Supple, Richard Keogh, Dennehy, McFaul.
Booked: Garvan.
Att: 31,473