"The violence of the comments for a kid ... We are really reaching the bottom. It would be a question of recovering a little," wrote the 23-year-old Parisian.
"I also wish you a happy new year my little Camille. Continue to fight as you do, you are giving us all a lesson in life", he commented.
Mbappé shared a tweet from the Breton association "A smile for Camille" which helps children victims of congenital and genetic diseases.
He compiled offensive tweets targeting Camille, 8 years old, who in a video posted on Twitter on Sunday, asked the player to "stay at PSG and continue to make us dream for a long time".
The future of the French international, whose contract binding him to Paris expires in June, is the subject of intense speculation.
"Camille the courageous little warrior just wanted to declare her love to @KMbappe. We could never have imagined so much hatred. The sadness we feel tonight is equal to this violence," wrote the association.
In an interview with the American channel CNN broadcast at the beginning of January, Mbappé spoke about the online harassment he suffered after his failed penalty shootout against Switzerland at the Euro which caused the elimination of France from the round of 16, last June.
"It was my fault, but receiving these kinds of messages, it hurt me. (How do I end it?) It starts with social networks. But first, we players, we must be involved. We must not not wait for that (insults, editor's note) to come to you. You have to be active to help people. For me, it is not possible in 2022 to have this kind of attitude ", he declared .
© 2022 AFP