Besides the Irish Soldier Laddie and The Irish Soldier Boy mentioned above by George Seto, I know of no other song except this one titled " The Dear Irish Boy" about a lad going off to war. I will post it although I don't think it's the one you are after.

THE DEAR IRISH BOY

My Connor, his cheeks are as ruddy as morning
The brightest of pearls do not mimic his teeth
While nature with ringlets his mild brows adorning
His hair, Cupid's bow-strings and roses his breath

CHORUS

Smiling, beguiling, cheering, endearing
Together how oft o'er the mountains we strayed
By each other delighted
And fondly united
I have listened all day to my dear Irish boy

No roebuck more swift could fly o'er the mountain
No veteran bolder meet danger or scare
He's slightly, he's sprightly, he's clear as the fountain
His eyes beaming love; Oh! he's gone to the war

Chorus

The soft tuned lark, his notes change to mourning,
The dark-screaming owl impedes my night's sleep
While lonely I walk in the shade of the evening.
Till my Connor's return I will ne'er cease to weep

Chorus

The war being over and he not returned,
I fear that some dark envius plot has been laid
Or that some cruel goddess has him captivated
And left here to mourn his dear Irish maid

Hope you like this one anyway.

Slainte ^^