I had two nephew birthday parties this past weekend. One I told you about here, the other was a first birthday for my cousin-nephew (technically he's my 1st cousin-in-law once removed, but that's confusing and he feels more like a nephew, so that's what I refer to him as).
I made them the same card, just changed the age (yeah for multi-age style cards). This was a design idea that I found on the Silhouette Flickr stream. I highly recommend checking it out for ideas.