Green’s Dictionary of Slang

(US) a supporter of political reform; also attrib.

1895		in T. Roosevelt Letters I 466: The Goo-Goos [...] have attacked me.
1907		H. Lawson ‘The Song of the Doodle Doos’ in Roderick (1967–9 II) 235: For this is the song of the Goo-Goo push, and the city-bred yahoos.
1933		(con. 1890s) C.W. Willemse Cop Remembers 82–3: The new men [police recruits] were called ‘Goo-Goos’ or if they were American born, a rare thing in those early days, they were known as ‘Narrow-backs’.
2002		at nationalpolitical.com 21 Mar. 🌐 ‘Goo-goo’ (good government) groups have been wishing for campaign finance reform for years. [...] But will the ‘goo-goo’s’ really get what they wished for?