The larger LEGO product line that invades Bricksburg in The Lego Movie is DUPLO.
The invasion occurs at the end of the first film, after Emmet and the other characters have defeated Lord Business and the LEGO world appears to be at peace. In the live-action framing story, Finn's father allows Finn and his younger sister Bianca to play with the LEGO collection together. Bianca then introduces her larger DUPLO blocks, which appear in the animated world as strange, oversized aliens.
DUPLO is LEGO's product line designed for younger children. Its bricks are substantially larger than standard LEGO bricks, making them easier for small hands to handle and less likely to be swallowed. Despite their size, DUPLO pieces can connect with many standard LEGO bricks.
The scene is also a setup for The Lego Movie 2: The Second Part. What first looks like a hostile invasion becomes part of a story about siblings learning to share their toys, creative ideas, and play space.