Like Carlee, it's also birthday season in my house (we come from the same family, where summer is always birthday season). To brighten up the house for the past few birthdays in my house, I made an easy paper flower garland. This was a project that my four year old daughter and I did together. My decoration isn't purely for birthdays, or long lasting, but it was a fun project for kids, and something that you can easily make to decorate for any occasion.
The idea for this quick project came from the Usborne book 50 Rainy Day Activities. (It's a great little book kid's art book, by the way, as are most Usborne books).