The 3 British soldiers who died as a result of the raid on Monk's Bakery where Kevin Barry was captured were :
Private Harold Washington, aged 15 (born Salford, Lancashire on 4th October 1904). Died at the scene of the raid.
http://www.cwgc.org/find-war-dead/casualty/378591/WASHINGTON,%20H
Findagrave
Private Marshall Whitehead, aged 20, born 3rd quarter (July to September) 1900. Died of wounds.
http://www.cwgc.org/find-war-dead/casualty/2751877/WHITEHEAD,%20MARSHALL
Findagrave
Private Thomas Humphries, aged 19. Died of wounds.
http://www.cwgc.org/find-war-dead/casualty/411232/HUMPHRIES,%20T
Findagrave
A wide range of propaganda was generated re the young age of Kevin Barry. The British don't appear to have countered this propaganda very well - there doesn't appear to have been too much done to use the age of Private Washington in relation to pressure re Kevin Barry's age (Harold Washington's death registration lists him as 19).