I found these on the Vodafone Ebay Store last week. I've bought some for my little ones and they seem reasonable quality, especially for the price. The £4.99 includes postage, they are also running a 10% discount if you buy 2 or more (just add them to the basket before clicking buy).
There are a few different styles, also noticed another seller with ladybird ones.
** Please note, as of today (20/12/16) Alien and Penguin and Monkey models are now £9.99 **
The sellers blurb...
My Doodles Children's Character 85 dB Limiting Headphones - Monkey
Have fun listening to your music
Have fun with these My Doodles headphones, perfect for listening to your favourite music. With their super-comfy fit and volume-limiting technology to protect your ears, our colourful characters have been designed to deliver you great sound in a fun way.
Fun character design
Cheeky Monkey! These headphones allow you to enjoy your music and look great at the same time
Prevent the sound from getting too loud and keep your ears well protected without losing sound quality.
Take with you anywhere!
The headphones' lightweight and foldable design makes them perfect for placing in your rucksack, so you can have music wherever you go!
Comfortable swivelling earcups
With an adjustable headband, soft-touch material and comfy earcups, we've done our best to make sure you can listen for as long as you like with no discomfort.
About My Doodles:
At My Doodles we're all about making everyday things more exciting, which is why we've created a range of friendly characters and handy accessories to unleash your imagination. Designed to keep you company on your adventures, whether you're exploring at home or outdoors, we've made sure that My Doodles is always around to brighten your day.
Frequency response: 20 Hz - 20 kHz
Sensitivity: 85 dB
Drivers: 40 mm dynamic
DC input voltage: 0.178 V
Jack plug: 3.5 mm
These headphones cost a few bob more on Amazon. https://www.amazon.co.uk/My-Doodles-Headphones-Compatible-Smartphones/dp/B00NLAJWVY
and the reviews are mostly favorable.