What's wrong with my son sitting in the car in the front of cart? He is 2.5 and LOVES to drive the car. I don't think they are reserved for people with only 2 or more kids with them.
I don't know what you mean by double carts but we have the carts with the cars in the front and then ones with the car in the back where you push and the actual cart in front.
I never thought, in a million years, that I was offending someone when using those with my ONE child because he loved them. I have seen plenty of people using them with just one child.