They are two young girls from two very different worlds, linked by a global industry that exploits an army of children.

Olivia Chaffin, a Girl Scout in rural Tennessee, was a top cookie seller in her troop when she first heard rainforests were being destroyed to make way for ever-expanding palm oil plantations. On one of those plantations a continent away, 10-year-old Ima helped harvest the fruit that makes its way into a dizzying array of products sold by leading Western food and cosmetics brands.

Ima is among the estimated tens of thousands of children working alongside their parents in Indo...