My littlest one just turned six, and requested a Lego Ninjago party. All of the decorations I found online were so dark, that I decided to primarily focus on the lego part of it, and just decorate with ninjago pictures they can put up on their wall afterwards. It was a total success!
Note to future me:
Putting together that many legos for the cupcake stand was torture.
Assembling all those characters was also torture. They came in like six pieces.
End of note.