Across Five Aprils Question in Chapter 9

What type of irony is this and why is it ironic: “And what was it that man said the day of the barn-raisin’? ‘It’s good that you’re a boy and don’t have to worry yourself about this war.’ Why yes, no doubt about it, eleven-year-old boys ain’t got a thing to worry about; this year of 1863 is a fine, carefree time for eleven-year-old boys…”?