At 5 they don't need structure and healthy 5 year olds can easily run a mile.

I don't think many 5 year olds could run a mile without stopping a few times.  

My last 5K there were a bunch of 4-10 year olds toeing the line. My dad was my "cheerleader" at the race, he walked with me to my starting point (I lined up with the 10mm crowd) and then he walked up to the starting line. My dad said the RD or a volunteer or someone was talking to those young boys in the front warning them if they can't run a 6mm they should move back because they could get really hurt. They all assured him they could and laughed. After my dad saw me cross the start, he went to the finish (it was a loop course, the finish very close to the start) and he said he saw all of those boys cross the finish in 20 minutes or less....several of them (who looked about 7 or 8) crossed in the 17-18 minute range. You'd be surprised at how fast young kids can be for pretty decent distances for a young kid. I don't think a child should go running a marathon or anything....but if they're not being forced, and not being over worked and over trained to the point that it is detrimental to their health or getting in the way of them "being a kid" I see no problem with him racing a few one mile races at age 5 or "training" for them as long as he is never forced or pressured into it, and by "training" it means doing a few fun runs during the week.

Kids aren't as stupid as adults.  They'll quit before they hurt themselves.  Plus, it's ok to let him make mistakes.  You can tell him all you want about not going out too hard and blowing up but he probably won't pay too much attention until it actually happens.  When it does happen, it's still no big deal.  Whatever keeps him happy and enjoying it is what is important.

 

I have two daughters, ages 7 and soon to be 3.  I see parents spending insane sums of money on dance for their girls when the reality is that not a single one of those kids will be a professional dancer.  We chose the dance teacher our kids go to specifically because she takes a much more laid back attitude.  I was talking with her one day and she said that in her 30 years of teaching, she has had precisely 2 kids come through that had the talent to really take it to a professional level.  

 

Maybe it's just my parenting perspective but I think it is far more important to let kids be active and explore various activities rather than pushing them to excel in any particular one.  They'll discover their talents in due time.

 

BTW, in my avatar is my 7 year old finishing my 50 mile birthday run with me.  That was by far the best running experience for me with the possible exception of running with her in her first 1K.

Same goes for adults...some things you've just gotta learn the hard way! 

And it will be fine for them to discover their talents that way unless they are going to some gigantic, Texas, suburban HS. Then they had better be training by their time they are 2 (yes, exaggeration) if they want to make the HS team, dance or cheer squad, choir, or drama group.  The competition is hell!

Another helpful site:

http://www.justrun.org/JR_for_kids/fitness_and_running_tips_for_kids.htm

and 2 good articles on the subject:

http://www.riverrunfororphans.org/blog/how-to-train-kids-to-run-a-mile/

http://claimyourjourney.com/2012/10/kids-and-running/

You'd be surprised.  My 6-year-old runs 5k's.  Easily.

Okay... that's one.

My son went out and ran a 1 miles race in 11 minutes 1 week after his 5th birthday.  He only runs when he wants to.  He loves to run, but I don't take him running with me.  He runs ahead of us on the trails when we hike, runs in the yard, and runs when we play Wii.  But he doesn't train.  I will say that he can pace himself much better than most his age, but all that means is that he runs the same steady pace the whole time while his peers sprint and then walk.  They all finish and have fun.  That is what it is all about.  I bet you will be shocked if you just let him do it.  My son started running "races" when he was 3.  We just let him do his thing.  It is about having fun and nothing else.