Given that the Others’s motivation is “extinguish everything we would call life,”” and that they “hated iron and fire and the touch of the sun, and every creature with hot blood in its veins,” I’m going to guess they killed them like they do all warm-blooded creatures.
This has been another PSA that no, the White Walkers are not good guys, the Night’s King is not evidence of a peace treaty that ended the War for the Dawn, stop it already.
If GRRM wanted us to think that the rise of Night’s King was a positive development, he wouldn’t have made the Nightfort one of the most haunted-ass places on a planet full to bursting with haunted-ass places. Honestly, if you don’t recognize the Others as evil fairies out to steal your children and kill your livestock like evil fairies tend to do, ya need to read more fairytales.
The Nitght’s Watch will be in real trouble when the White Walkers’ army of zombie sheep shows up.