At NatWest's London headquarters, Princess Diana met with nine prominent companies, including Lego and Ikea.
Middleton's "Shaping US" campaign promotes early childhood's impact on life.
She advised corporate executives to encourage their employees to improve the working environment and the learning environment for children.
Middleton said that societal change is only possible with the support of powerful business leaders.
Dame Alison Carnwath, CEO of NatWest, says the economy and children grow together.
Middleton's white Alexander McQueen jacket, who designed her royal wedding gown, is her latest.