I've done the Strathcarron Hospice 10K at Denny Central Scotland twice with our son in his BabyJogger. Times were 2 mins slower than running without. They also allow dogs too. First time I started right at the back, but it was more of a hazard overtaking half the field in the first 2 miles, so next time I started just a little further back than I normally would, but kept well to the side of the field.