Russo Music or Zeswitz Music both provide quality rental instruments!  You may choose any other rental vendor as well.
    Most 4th graders play the following sizes:
    violin:  1/2
    viola:  12"
    cello:  1/2
    If your fourth grader is larger than average, go up one size to 3/4 violin, 13" viola and 3/4 cello. 
    If your fourth grader is smaller than average, go down one size to 1/4 violin, 11" viola and 1/4 cello. 
    Most 5th graders play 3/4 violin, 13" viola, and 1/2 or 3/4 cello.