Tempo is how fast or slow the beat should go in a song.
Tempo is measured in beats per minute (bpm), such as 60 bpm, or using words that describe how fast, such as adagio (slow), moderato (medium), or prestissimo (very fast). (Presto is fast, but it is easier to teach these three terms because they are approximately in an equal ratio to each other: 60 bpm, 120 bpm, and 180 bpm, respectively. That means 1, 2, or 3 beat per second).
Here are links to ideas for teaching tempo (slow, medium, fast, or adagio, moderato, and presto):
DMK Tempo lesson 2-27-15 (Mrs. Y’s)
Other links to lesson plans on teaching tempo: