We had a Lego party for my son's 10th birthday.  I printed invitations on my computer and used wording that you would find on a construction work order. (Project (10th Birthday Sleep-over), Foreman (Child's Name), Building Material (Legos), Construction Date, Construction Site, Necessary Equipment (pillow and sleeping bag), Demolition (when party ended) and Order Confirmation (RSVP). I sized them so they would fit on a flat stack of Duplo Blocks. After I printed them, I glued one onto a stack of blocks with rubber cement, then I used a craft knife to cut it apart. An instant Lego puzzle! I mailed them to the guests broken apart so that they had to put them together to get the party details.         For the party, I bought yellow construction caution tape at the home center and used it instead of streamers.  I purchased construction hats for each of them from Kipp Brothers ($1/ea).  I made a Lego piñata with a box and cut up cups for the knobs.  I also, of course, had piles of Legos and lots of primary colors for the plates, cups, etc.. The cake was a sheet cake with 8 cup cakes on top to make a Lego. For dinner, they "constructed" their own pizzas and for a snack, they "constructed" an ice cream sundae.      We had races to see who could build the tallest Lego tower in 30 seconds.  I found some small, inexpensive Lego sets ($2) at a discount store. I gave each child a set, without the instructions, and had them see what they could come up with, then we had races with the results. (I did eventually give them the instructions. Some of the children weren't as experienced with Legos and got frustrated quickly.) They took the sets home with them along with the candy from the piñata and some Lego blocks candy that we purchased (kind of like sweetarts, but you can build with them!).