Sing the word using the song to match the number of letters:

1 letter: Frere Jacques
I spells I
I spells I
Listen to me
Listen to me
I spells I
I spells I
Listen to me
Listen to me

2 letters: If You're Happy and You Know It:
If you're happy and you know it spell at:
A-T
If you're happy and you know it spells at:
A-T
It you're happy and you know it
Then your face will really show it
If you're happy and you know it spell at
A-T

3 letters: Mary Had A Little Lamb
Spell the word and 
A-n-d  a-n-d  a-n-d
Spell the word and 
a-n-d all day long.
Repeat

4 letters: Clementine
S-a-i-d  s-a-i-d  s-a-i-d
Spells said
s-a-i-d  s-a-i-d  s-a-i-d
Spells said
Repeat

5 letters: Bingo
6 letters: Happy Birthday