George, who turns 5 in July, and Charlotte, who turns 3 next week, were brought to St. Marys Hospital in London by their father, Prince William.
George arrived dressed in his school uniform, while Charlotte wore a floral dress with a sweater.
Both children held on to Williams hands as they made the short walk from their car to St. Marys. Charlotte turned around and gave a wave as the family entered the hospital.
The boy, whose name has not been announced, weighed 8 pounds, 7 ounces, according to Kensington Palace.
William, 35, was seen leaving St. Marys Hospital just a few hours after the babys birth was announced publicly.
Williams return to the hospital with his two older children was greeted by cheers from the crowds of fans gathered outside St. Marys awaiting the new babys birth.
The new baby is now fifth in line to the British throne, following George, third in line to the throne, and Charlotte, fourth in line to the throne.
George and Charlotte both currently attend school near Kensington Palace, George at Thomas's Battersea and Charlotte at the Willcocks Nursery School. It is expected that Kate and William will initially enjoy solo time with their new infant at the palace.
Apartment 1A in Kensington Palace in London is the family's official home.