This is the song Ricky Gervais sings to Elmo on the DVD "Elmo's Animal Adventures"

Chords Used:
Am: x02210
F : xx3210 (Or 133211)
C : x32010
G : 320033

 Am                 F
The letter 'N' is what you need,
 C               G
When you take a nap,
 Am                  F
Need to put your nightshirt on,
    C             G
Or put on your nightcap.

 Am           F
'N' begins nummies,
            C             G
Which are really nice to eat
Am                    F          
At night before you nuzzle down,
      C          G 
In between the sheets

'N' goes:
Am      F          C          G 
NNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNN

'N' goes:
Am      F          C          G
NNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNN


 Am               F
When you want to rest your body,
 C               G
Lay your noggin down.
 Am            F
Put on your pyjamas
    C              G
Or put on your nightgown.
 Am                  F
Tell your niece and nephew
            C                  G
And the neighbours down your street
      Am          F
The letter N is really helpful 
 C                 G
When you need to sleep


And 'N' goes:

Am       F         C        G
NNNNNNNNNNNNNNNNNNNNNNNNNNNNNN (x 4)

''Nighty night!''