Rhythm will start to make more sense to your students as they get better at feeling a steady tempo. Use a metronome or click of some kind to keep the pulse steady. Try to get the students to ingrain and feel the pulse of different tempos while using the click. But make sure you pick a day to play without the click as well or the young musician will become too dependent on the metronome. Have your students clap, tap, stomp, count or play the basic fundamental rhythms at a few different tempos each day. Then on occasion have them create their own rhythms and choose their own tempos to play with the ensemble or challenge each other.