Is a child who can remember multiple world capitals from a very early age very intelligent?
Parents are relatively often proud of their children's abilities and skills, especially when they stem from aptitudes they once wished they had. Just watch them in their own child's school presentation. Just as soon as the child raises their hand, dances, draws a few doodles, chases a ball, or recites in a halting voice, the parents applaud, take photos, and rejoice, as if they were truly witnessing a high-level artistic, literary, or sports presentation. Not to mention when the child already gives relatively complete performances in art, sports, or science. It seems as if the parent is actually applauding themselves.
One of these versions of self-praise consists of presenting the child in front of larger audiences performing antics. In its more commercial version, the child appears as a clown reciting or acting. Learning the world's capitals is often one of the favorite activities for parents who want to take advantage of a memory skill present in some children. This ability corresponds to a psychic process so simple that parrots can partially develop it.
Consequently, it seems quite absurd to assign a child with good memory skills to a task as insubstantial, routine, and short-term as remembering flags or capitals of the world, an activity that fortunately has begun to be abandoned even in the most traditional schools around the world.
To go deeper: Contemporary theories of intelligence and exceptionality