I bought these for my son when he turned three in August (because I loved the look of them) and I am pleased to say - he loves them too.
I fix them to his paper with a small bit of sellotape at the top and bottom - which can easily be peeled off when finished, this prevents them from slipping around which can be very frustrating for him!
When drawn in, he then spends time colouring them and embellishing them with felt shapes, feathers, sequins etc.
He has spent hours with these since he got them (my bigger boy likes them too) - his particular favourite is the dinousaur, of course.
They are made by Djeco, a French company, who make lots of fab toys, I love everything in their art and craft range. There are lots of other sets available from dragons to princesses (check out the range at http://www.tickety-boo.co.uk/, one of my favourite independent online toyshops), I think Father Christmas might have a few more tucked away in his sleigh for our house this Christmas!