Henry Kavanagh was born at Rock Big, Arklow on 23 February 1914, the eldest child of William Kavanagh and Sarah Mary Dunne. His birth was attended by local midwife Sarah Massey of Fairgreen and officially registered on 8 April 1914.
Henry was born into a close-knit network of families spanning Rockbig and Askintinny. He was named after his paternal grandfather.
During his early childhood, Henry's family resided at Rockbig before temporarily moving to Money Big and Abbey Street.
On the night of 18 April 1926, Henry was recorded living in the townland of Ballinabanoge, Co. Wicklow, with his parents and siblings; James, Mary and Elizabeth.
Henry was listed as 12 years and 10 months old, born at Rock Big, Co. Wicklow and attending the local school.