Lyrics:

Hello children, it's time for an important lesson with Professor Flans.
This is about four letters that people sometimes confuse for one: LMNO!

LMNO
Are four letters
LMNO
Are not one

L
L M
L M NM N Ohhhhhh!
LMNO
L M N Ohhhhhh!
LMNO

LMNO
Are four letters
LMNO
Are not one

LMNO

L M N Ohhhhhh!
LMNO
L M N Ohhhhhh!
LMNO