Green’s Dictionary of Slang

(Irish) a bald-headed, or very short-haired, person, thus a baby.

1896		Sporting Times 24 Oct. 2/5: ‘Scaldy Bill’ Quinns [...] has lately blossomed out as a fighter.
1996		(ref. to 1930s) Irish Times 12 Apr. n.p.: Growing up in Belfast in the 1930s a baby in the nest was always a scaldy – what else could one have called it [BS].