Definition of "kinder"

Electric trains have much lower operating costs and are kinder to the track.

2021 February 10, Nigel Harris, “We risk destroying value”, in RAIL, number 924, page 3

I told ’im to give you the strings last night, but I’m kinder glad thet Rosebud interfered an’ saved yer life.

1882, James Jackson, Tom Terror, the Outlaw‎

'No, he was kinder reticent about that part of it.'

1934, Agatha Christie, chapter 9, in Murder on the Orient Express, London: HarperCollins, published 2017

But - let wifey leave him with the kinder while out shopping...

2008 December 31, Al Scaduto, They'll Do It Every Time (newspaper comic)

Of special interest to the kinder are The Children's Place, Baby Gap, Gap Kids and Gap, Gymboree, The Limited, America!, and the Sweet Factory.

2010, Beth Rubin, Frommer's Washington D.C. with Kids, John Wiley & Sons

Do note, as Goin mentions, this is a policy better implemented when the kinder are well past infancy.

2012, Charlotte Druckman, Skirt Steak: Women Chefs on Standing the Heat and Staying in the Kitchen, Chronicle Books, page 192