I'm having the exact issue that Nick is describing. I'd say my kids basically only view Youtube, but b/c Koala tracks background usage, it looks like they're on for hours.
Looking at their history, it seems like the Youtube app/browser is communicating with youtube every 5 or 10 minutes when the browser tabs are open.
I can send you the profile name, device name and login email to you in a private channel.
p.s. thanks for the awesome support so far.