I'd agree with Lefty on this one; relay races are excellent sprint training for younger ones and you can control the distance/time very easily whilst keeping it fun and competitive. I think that any speed training above 30sec intervals is ineffective for this age group; they will all be pre-puberty and not ready for lactate threshold training anyway; better to keep it short and snappy to encourage good form instead.

We tend to run two different kinds of session for this age group;

  1. steady long run on the fell to improve aerobic fitness and agility; nothing so steep that can't be run even at a slow pace, reasonably uneven to encourage awareness of foot technique and core balance.
  2. Indoor 'game' based sessions; focussing on short interval efforts, sprints, direction changes, lateral movements etc.