There are options available for single or multiple bikes and varying ways of attaching the bike with clamps and/or straps. Some brands are specific to particular car manufacturers and models, others to car styles (hatch-back, boot, estate etc). A small amount of investigation regarding your particular car is advised before purchasing and many car rack brands offer information on compatibility.
Trailers are available for carrying small children or for moving luggage etc (touring or everyday use). They attach simply and quickly but riding style must be adapted to accommodate the extra width and weight. For the older child who is not quite ready for independent cycling, the tag-a-long is ideal. Tag-a-long bikes attach to the rear of the adult bike and enables the adult rider to ride for longer knowing their youngster is safe, can keep up and is not able to stray..