As stated above, it all depends on the child. DD (5) has always gone running with me, but I go at a slower pace when I’m with her. Some people get upset with me when I tell them this, but my guess is that they are jealous because I am slim and fit, and most of them are fat slobs. They shouldn’t be getting mad, they should just eat fewer pies.

Anonymous wrote:OP here -- thanks everyone. My kid isn't even 3, I was just wondering when he might be old enough to enjoy this. And some 5Ks are definitely family-friendly.

A lot of races will offer a 1 mile or 1k version of the race for kids.

PR races in northern VA has a lot of them. Here's an example of one coming up that is super hero themed, so it could be fun for a young kid.
https://potomac.enmotive.com/events/register/2019-guardians-of-education-5k-super-hero-fun-run

Another place to check for these shorter kid fun runs are when the local elementary schools have 5ks. I know a lot also do a 1 mile fun run.

PP (9:28) We don't run races but we are a family of hikers. We have had our son, 7, out camping since he was 4. He completed his first backpacking trip this summer. 5 miles with a 12 pound pack (with water and within the weight ratio recommended for kids, he is in the 95th percentile for height and weight). He loved it and has been asking when we can go backpacking again. He regularly goes on 3-6 mile hikes with us and will ask to go out for hikes. We went camping with friends and their child, a friend of mine, was whining about the hike 1 mile in. Different kids have different interests and that is fine. What seems early for you might be something that another kid that same age loves.

So I can buy that there was a 4 year old whining at a 5K race, I can also see that there are 4 year olds who will have fun with such a race. You don't know until you try.