West Ham Vice-Chairman Karren Brady was on hand to meet and greet and show the royals around the stadium.
Kate accepted personalised West Ham shirts for Prince George and Princess Charlotte from Mark Noble and Slaven Bilic.
Mark Noble said: “It was just a little gift from West Ham really. We know William is an Aston Villa fan – whether they [the shirts] will get put on or not, I don’t know. It’s just a gesture from us to welcome them to the club.”