One of the first sings we sing to demonstrate the length of half notes is Frere Jacques (Are You Sleeping?). I sing it first, and students raise their hands when they hear the long words ("John" and "dong"). Then I draw the beats of the song on the board like this:
Then I point to the beats while the students clap the rhythm of the song (each line repeats). Ask students to find which beats are the long sounds. "Tie" the beats together.
Then turn the tied notes into half notes and teach them the name of it.
Add note heads to all notes. Tell students they just turned the BEAT into the RHYTHM!