"We are all working to give children the emotional strength they need to face their future lives and thrive."
Kate, who is royal patron of the charity Place2Be, had been spending the day at the school leaders forum in central London.
The event will see expert speakers consider how schools can provide practical support to children, young people and their families.
The Duchess, who is pregnant with her third child, has attended the past two conferences hosted by the charity.
Kate has been stepping back into the limelight after suffering from hyperemesis gravidarum, a severe form of morning sickness.
She is in her second trimester, with the royal baby due in April.