I just love a Colourful Coaster and came across these Via Inspired by Charms Blog post.
Take a look at there tutorial ( Link below ) ~ you can also make your own felt balls if you want to go totally DIY on this using pure wool, soap and a lat of elbow greese !!
I will probably find a separate tutorial to post for the actual felting but this link is a super idea and perfect for the kids to dive in on too.
Here is the Link to the Tutorial Via Inspired by Charm :
( If the Link does not go straight through ~ copy and paste into your browser )