For my son’s 5th birthday, we had a Lego theme for his party. He had gone to Lego Land for the first time about a month before his birthday and became totally obsessed with Legos! When we decided on the theme, I assumed that I would have to make some decorations, and buy some decorations. Turns out that there’s not many Lego party items out there for sale! So, most of the decorations, we I made myself.
Even the cake, I converted to be Lego-ish! The only custom-made Lego cakes I found were over $100, and I think that’s ridiculous to pay for some 5 year-olds. The bakery at my local grocery store promised to make something I would like, and she didn’t disappoint me! I added some Lego men and some Lego candy.
I bought the party-themed Legos from the Lego store in the mall and placed them in front of the cake. Our guests really thought it was a Lego cake!
I also made Lego masks- male and female ones- for our guests. The kids didn’t keep them on long, but they ALL made sure to take a mask home with them!
I found the idea and template here.
The kids mostly wanted to play outside, or watch the Lego movie, which I had playing on repeat the whole time. I was able to round 5 or 6 kids up to come over and play “Pin the Head on the Lego Man.”
Another thing to keep the kids busy, especially the smaller ones, was this Lego coloring poster. I created it on my computer and paid about $5 for Staples to print it on engineering paper. The kids colored with Lego minifigure crayons, which they also took home as party favors: 
The Lego head hanging above the poster was made with yellow paper lanterns and black and white construction paper. You can find the instructions here.
Each plate and cup had a different Lego face drawn on it. I used my son’s Lego container to hold snacks. I also had cheese puffs container that I painted yellow and used the same construction face as the lanterns to make another snack holder:
I bought 5 of these $1 frames from Ikea, and put “Lego-ized” photos of my son in them. I used some effects in Photoshop. I did so much, I don’t remember what effects I used!