We had a Lego-themed party for my son's 7th birthday.  The theme colors were red, yellow & blue. On the invitations, we asked the guests to dress in those colors. Streamers, paper plates, napkins, & balloons were in these solid colors. Invitations were made from construction paper (in the 3 colors) in the shape of three attached Lego bricks.  The cake was also in this shape, with frosting in the 3 colors, and the top edge cut out to resemble the Lego "knobs."     I bought a 1200-piece tub of basic Lego bricks, which we dumped out into the middle of a large table and used for the various games:   Guess What I Built:  make simple picture &/or word cards (house, car, robot, etc.) & drop into a hat or box. Let each child pick out a card and tell them not to show it to anyone else.  Then each person builds what is on their card.  The others try to guess what each creation is.    Timed Building Game:  choose one thing to build from the above-mentioned cards.  Everyone has 5 minutes to build that item.  Judge the results and award prizes for fastest builder, largest creation, most detailed, most colorful, etc., (so that everyone gets a prize for something.)   Timed Tower: who can build the tallest Lego tower in 3 minutes?   Lego Relay Race: Use a large Lego brick for the hand-off.   Favor bags included inexpensive Lego sets, along with treats.