It's also important at young ages for the activity to not be excessively competitive. Some children enjoy competition. However, many other children, when not able to rise to the level of the competition around them, will withdraw from an activity. It is also important to remember to stop the activity before it becomes totally exhausting. A 20 to 30 minute period of riding bikes with Mom is sufficient for a 7-or 8-year-old; it does not have to be an hour and a half.
It's hard to say how coordinated or uncoordinated a child will be later in life. Probably most children who start out very physically coordinated will continue to be reasonably coordinated as adults, presuming they do not become excessively overweight and don't have any severe injuries. However, children who are physically uncoordinated are not necessarily going to be "klutxes" as they get older. There are a lot of changes that occur in a child's body as he grows and particularly as he goes through puberty and reaches adult size.
Different sports require different types of coordination. A child who seems to be very uncoordinated when trying to play soccer may be a very good and coordinated swimmer, where footwork is not as essential. A child who seems to have difficulty with tennis or baseball may not have very good hand-eye coordination, but may be very good at gymnastics or skiing, where balance is important. By observing your child over time, you should be able to get a sense both of what he is interested in, and what his strengths are. This can steer your choice of physical activity.