Child of the Earth

The Child of the Earth is a treasure found in Pikmin 2 and Pikmin 4. It is actually a.

Collecting the treasure in Pikmin 2
It's found in sublevel 3 of the Cavern of Chaos buried underground. White Pikmin are needed to dig it up. There are multiple Creeping Chrysanthemums and Mamutas which will disturb you if the treasure is carried back to the pod too early.

Sun-Speckled Terrace
There is a Child of the Earth completely buried near the north-middle section of the overworld, just before the summit with the wheel. It can be located more precisely with the Treasure Gauge or by searching for treasure using Oatchi. To collect this treasure, you must throw 7 Pikmin in its vicinity so they can dig it up.

Engulfed Castle
There is a Child of the Earth half-buried and partially submerged underwater in the northern room of sublevel 3 of the Engulfed Castle. It is guarded by a Wollyhop, which should be defeated before attempting to collect it. To collect this treasure, you must throw 7 Pikmin at it.

Trivia

 * Although Olimar claims he has never seen a potato before, it is clear that potatoes are known to Hocotatians, given that Louie's notes for the Emperor Bulblax mention the vegetable. It is, however, possible that potatoes on Hocotate are different from those on Earth.
 * The name is likely a reference to the French word for potato, pomme de terre, which translates to "apple of the Earth".