Assess the musical knowledge of your students. Ask them if they know what rhythm and melody are, if they can sing scales, and if they can read sheet music. A group of musically literate glee club members will be easier to teach songs to compared to a group of students with no formal musical training, although the process is basically the same.
Play the songs on your stereo system or computer so that the children know what they sound like. While it is possible to pick up a song just off of sheet music and lyrics, learning to do this is a long process requiring vigorous training. However, a child who has no idea how to read music can learn the melody of a song by listening to it and singing along with the teacher and other students.
Distribute lyrics sheets to your students. Memorizing lyrics is challenging for even seasoned musicians, and professional choirs use lyrics sheets extensively. When teaching children who may not be musically literate, lyrics sheets are even more important, since the words will provide these children the cues for changes in tone and rhythm that they cannot see in musical notation.
Sing the song for the students one section at a time, and have them sing along with you until they can sing the section without you. It is up to you how many sections you break the song down into, but the shorter the sections the easier it will be for students to master them and move on.
After the students have learned to sing all the parts of the song, have them attempt the song from start to finish. Likely, they will stumble in the transition between certain sections. Focus on these sections and then try singing the song from the top again. Repeat until the students can sing along with you from start to finish.
Have the students sing the song from start to finish without you. You can mouth the words to show them what they should be singing, but the end goal is to have them singing the song independently as a group.