I was watching Fetch in our bedroom yesterday morning and saw that CN and Boomerang were now available.
From their Facebook page:
25 January at 15:14 ·
Cartoon Network and Boomerang have arrived on Fetch TV.
All our customers can enjoy them free of charge until 27th February 2017.
You don’t need to do anything, just go to CH155 and CH156 in the TV Guide and start watching.
If you don’t see them yet, simply restart your box at Menu>Manage>Settings>Device info>Options> Fetch TV box restart.
During the free trial the channels aren’t recordable and are not available via the app.
Stay tuned for more info on what happens after the trial - it’s going to be exciting.