Green’s Dictionary of Slang

1. (orig. US) anything considered childish and/or insignificant or easy to achieve.

1899		Munsey’s Mag. 21949/2: A dull faced literary hack who offered to do ‘all the kid stuff’.
1910		Lippincott’s Mag. 85 333: He made us see how ridiculous and out-of-date it was to be wicked—what callow kid-stuff it was for grown men to play the brute.
1916		J. Lait ‘The Septagon’ in Beef, Iron and Wine (1917) 17: Kids are kid-stuff, anyhow.
1935		J. Conroy World to Win 230: Leo liked to josh her, too, but he was getting too old for that kid stuff.
1942		N. Algren Never Come Morning (1988) 67: Benkowski’s washed up. Barber’s just givin’ him kid stuff t’ do to kep him from messin’ around the big stuff.
1957		H. Simmons Corner Boy 39: That’s kid stuff [...] I’m too old now.
1962		(con. 1953–7) L. Yablonsky Violent Gang (1967) 31: For many gang youths drug addiction is a next step – when gang kicks become for them ‘kid stuff’.
1968		J. Barlow Burden of Proof 7: It was kid’s stuff to get in and break the rivets at the back of the safe.
1978		P. Theroux Picture Palace 108: Then it became small and unimportant, kid stuff.
1982		R.M. Brown Southern Discomfort (1983) 184: I went to a party last week, kid stuff.
1986		F. Taylor Auf Wiedersehen Pet Two 302: This was kid’s stuff to Moxey.
1997		L. Davies Candy 192: He wasn’t about to mess around with kids’ stuff.
2001		N. Barlay Hooky Gear 2: Even all this would be knockabout kids stuff.

2. pornography that features the sexual exploitation of young children.

1994		A. Vachss Down in the Zero 100: And we have plenty of women buyers for the [sex] videos. Some mostly buy kid stuff.
1997		‘Defenestrator’ PISS Publications 🌐 I’m not saying that porn is wrong (well kid stuff is) but I’m just saying that the media and the public in general has the wrong idea about the Net.
2000		D. McCumber X-Rated 147: I still think that mainstream widely available commercial adult material — not the kid stuff, not the fetish stuff— is so benign.