We found some nice material for them at the Ikea.
I decided to sew the pillow covers with an envelope-back because you can easily take the pillow case off of the pillow and wash it. I found great instructions on how to do so in my Overlock Die ersten Stiche book by Gaby Seeberg-Wilhelm.
Below, you can see what nice seams my overlock machine sews. : )
I hope my friend's daughter will like her pink pillows! : )