Hi Martin, In terms of fitness for under 13's I agree with other comments that recommend lots of small sided games and high activity levels or ball rolling time in sessions. Some things that can support high ball rolling time are arrival activities so the players are active as soon as they arrive, working in smaller groups, smooth transitions between practices and limited interventions from the coach. A wider consideration for u13 players related to fitness training is that they will be going through adolescent growth spurt at different times so generic fitness activities will have limited benefits until they are post puberty. Instead the recommendation is to focus on football activities which provide fitness benefits as a by-product. 

Hi Martin, In terms of fitness for under 13's I agree with other comments that recommend lots of small sided games and high activity levels or ball rolling time in sessions. Some things that can support high ball rolling time are arrival activities so the players are active as soon as they arrive, working in smaller groups, smooth transitions between practices and limited interventions from the coach. A wider consideration for u13 players related to fitness training is that they will be going through adolescent growth spurt at different times so generic fitness activities will have limited benefits until they are post puberty. Instead the recommendation is to focus on football activities which provide fitness benefits as a by-product.