Re: Kids on a leash.
I don't like them. I have taken a set of 5 year old twin boys, a 4 year old girl and a 6 month old to the park on my own before and I didnt need any safety straps.
Rules, awareness of dangers and consistancy with rewards/sanctions work just as well. You have prep the children before you go anywhere, even to Asda!
I find that the younger ones are easier to control. I once had a group of 5 9 year olds on a school trip, they were awful, were fully aware of the dangers of crossing a road without traffic lights but did it anyway! The little ones listen and are much easier to bribe!