Why isn't Star Wars a compound word?

For the past two days we have worked on compound words - our curriculum introduced the concept and the kids always have fun with putting little words together to make a bigger word.  I have these cool picture cards that fit together - two piece puzzles.  Each piece has a picture of a small word (cup, cake) and after you put the pieces together you flip over the puzzle and see a picture of the compound word (cupcake).  We went through every pair, identifying the two small words and putting the pieces together - skateboard, sunflower, birdhouse, jellybeans, lighthouse, starfish, etc.  Some of my students could barely contain their enthusiasm and shouted out the compound word before we even put the pieces together.  They loved it!  At the end of the activity I heard a bunch of students say, "That was SO fun!"

Today we reviewed compound words from yesterday and used them as our topic for writing.  I asked the students to think of their favorite compound word and draw their own pictures.  I modeled this for them on the board first.  Most of them could only draw the picture for the compound word and label it.  But I had quite a few who were able to draw the individual small words as well as the compound word and then label the pictures.  It's always so fascinating to see the varying levels of understanding.

I told students that if they wanted to choose their own compound word, not one we did yesterday, they needed to check with me before drawing their pictures.  Here were some "compound" words they wanted to draw:  Star Wars, acrobat, bow & arrow, pumpkin.  I had to explain to one little guy that while his picture was awesome, dragon is not a compound word.  Fortunately, he was equally happy to draw a cowboy.  Our language is very interesting.  Star + fish =  starfish is a compound word, but Star + Wars = Star Wars which is not.  How very confusing for little ones who are just learning what a word is.