Umm... having 2 youngsters who love to run and am a club runner myself I think I may be in a position to answer this.
My daughter is 8, going on 9 and in year 4. She's built like an athelete and comes along to my club training sessions each week whenever they're appropriate ( light evenings, she's in my sight, off the main road, etc.). She has recently twice been to Sunday morning sessions run by Reading Junior A/C in prep for March when the A/C starts again. She will then go every other week throughout the season (Mar-Sept) for fun and have a break during the winter months until she's in year 5 again during Mar - Sept.
Last night my 6 year old son came to training as the session was appropriate (flat ground, in my sight, lights etc.). I told him to run on the grass when possible, instructed him to relax, stop clenching fists, lower shoulders, stop looking around him, when to stand with the coach, etc. It was his first session and he LOVED it!!!!
My two children are both very energetic and to them it's natural that mum loves running and goes out frequently. For my children I have never connected running with staying slim but with being fit and healthy. It's something you can easily nurture within children whether it be taking them to a training session with you or just a quick run around the block when you come back from running.
