Well, we had a Playmobil themed party when ds was 8 (don't laugh stealthsquiggle), so I don't see why you can't do the same with Lego.
We played pass the parcel (you can put a Lego prize, and a small minifigure in each layer).
Dress the Playmo/Lego man (ds drew a picture of Norman the Foreman, we printed 2 of them and drew and cut out paper clothes, each team threw the dice and could add an item of clothing when they threw a 6, first team to dress man wins)
Pin the something or other on the Lego man/woman. (We had pin the teacup on Norman the Foreman)
Hunt the minifigure - hide minifigures round the room, whoever finds most wins the prize.
Drawing in the dark. This game can only be done of the party is late enough in the day. Sit everyone round a table, give them all pencil and paper, then turn lights off. Tell them all, bit by bit a (Lego-themed) scene to draw. then put lights on and laugh at everyone's pictures.