DUPLO (101 parts)
The larger bricks for younger kids are twice as big in each direction and compatible with regular LEGO bricks.
You can attach a standard LEGO 2×2 or 2×4 brick on top of a DUPLO brick. This allows you to create large models using DUPLO bricks for the core, with standard LEGO bricks covering them up.
Remember, twice as big in each dimension results in a brick that is 8-times as large by volume.
If that's not big enough, there's also the discontinued QUATRO line, which is 4-times the width of a LEGO brick (or 64-times the volume).
