Do you want to delete a channel you get?
- Does the bot have permissions?
var voice_channels = category.children.find(c => c.type == 'voice');
- returns first voice channel
If you want to get every channel, use:
var voice_channels = category.children.filter(c => c.type == 'voice');
Deleting a channel:
https://discord.js.org/#/docs/main/stable/class/Channel?scrollTo=delete
var voice_channels = category.children.filter(c => c.type == 'voice');
//Discord.js version 12 (I believe)
var channels = voice_channels.map(e => client.channels.resolve(e))
channels[1].delete()
//use client.channels.get(e) in older versions