Isn't this bunch of balloons birthday card just the cutest? Best of all, my 11 year old daughter made it for her brother, thus keeping up my family tradition of making birthday cards. I'll admit I did give her the idea of making a bunch of balloons, and adding actual strings, but that was my only input, and the results are just as cute as can be!
So do encourage your kids to make homemade cards, and if you have to help them out with an idea or two, so you absolutely should, and now you have at least one good one under your belt!
Note: My daughter used crepe paper for the balloons as that is what was right in front of her. It would be great to experiment with a bunch of different materials, though even colored card stock would work.