I like to use wall stickers to decorate a kids playhouse. They are fairly inexpensive and because they can come off the walls easily, you can swap them out as your child grows older and their decorating tastes change.
This link takes you to an example of Super Mario wall stickers. There are so many different wall stickers out there, it’s almost limitless. Check it out for yourself (the link is not an affiliate link).
I am a Mom of 3 kids who is a kids playhouse enthusiast. If you love kids playhouses too, then please check out Kids Playhouse Blog for the latest playhouse trends and fun activities!