So in this case I had 2 options: writing happy birthday on a simple piece of paper, or making something cute that children (hopefully) like.
I decided to consider the second option and this is the card I made!
It's a tiny box with a little birthday cake inside and her name on the cover. All of them are paper quilled.
This would be a nice idea for Valentine's Day too...instead of the cake, you could put a quilled heart inside the box!
I hope you like it :)