Ozil agreed to pay for 11 youngsters' treatment before the tournament began but has since pledged to support 12 more children, in line with the number of players in the victorious German squad.
The Arsenal midfielder, who played a key role as Joachim Low's men defeated Argentina 1-0 in the final, says the gesture is his way of thanking the Brazilian general public.
“Prior to the World Cup, I supported the surgery of 11 sick children,” he posted on his official Facebook page.
“Since the victory in the World Cup is not only due to 11 players but to our whole team, I will now raise the number to 23.
“This is my personal thank you for the hospitality of the people of Brazil.”
Each member of Germany's squad received €300,000 [£240,000] for defeating Argentina at the Maracana and Ozil's donation is part of the BigShoe project – whose goal is to help underprivileged children with medical needs.