Snowboard Kids 

All snowboards, characters, and courses 
At the title screen:
press Analog-stick Down, Analog-stick Up,
Down, Up, C-Down, C-Up, L, R, Z, Left, C-right, Analog-stick Up, B, Right, C-Left, Start.
If you entered the code correctly, Nancy will laugh.

Snowboard Kids 2 

All snowboards, characters, and courses 
At the title screen:
press Z, B, C-Up, Down, Analog-stick Left, Analog-stick Right,
Up, R, Z, A. If you entered the code correctly, Damien will laugh and spin off the screen.
All characters will be unlocked in battle mode and all 
tracks will be unlocked in story mode when a new game is started.
The code does 
not affect previously saved games.