The head of the federal euthanasia commission gave no details of the minor beyond saying it was an exceptional case of a child with a terminal illness, the Het Nieuwsblad reported.
"Fortunately there are very few children who are considered (for euthanasia) but that does not mean we should refuse them the right to a dignified death," Wim Distelmans told the newspaper.
Since its euthanasia legislation was amended in 2014, Belgium has been the only country in the world that allows children of any age, as long as they are able to make rational decisions and are in the last stages of an incurable disease, to choose to end their suffering.
The Netherlands also allows mercy killings for children, but only for those aged over 12.
The Belgian amendment, which was passed after heated debate -- notably over the meaning of a required "capacity of discernment" -- offers the possibility of euthanasia to children "in a hopeless medical situation of constant and unbearable suffering that cannot be eased and which will cause death in the short term".
Any request for euthanasia must be made by the minor, be studied by a team of doctors and an independent psychiatrist or psychologist and have parental consent.