Whoever wrote it ( and I have a variation that DOES Scan and makes a bit more sense ) it refers to that delightful period that so many staunch republicans seem to deny the existence of , when the I R A declared war on the Newly Formed Irish Free State after partition !

And we'll have little children , and rear them neat and clean
To shout 'Up The Republic' and to sing about Sinn Fein
The'll do what their old fellows did to Englands Power defy
Send them off with guns against the Free State Huns
      Down by the Liffey side