Hi Charlotte,
My feeling is that they were hired for excursions, though probably by a group larger than a family. A pub in Tunbridge Wells for example, hired one (possibly two) in Sept 1909 for a day's excursion through the hop fields to Maidstone. I also get the feeling that local church groups and societies did do things on a shared basis more than we do now, and picnics were popular.
Chris 1909