Acting ACT chief health officer Dr Vanessa Johnston said the child presented to a hospital emergency department on Friday.
ACT Health could not confirm the child's condition, but Dr Johnston said it was reminder for people to be careful around wild mushrooms.
"As the name suggests, death cap mushrooms can be deadly and all parts of the mushroom are poisonous whether they have been cooked or not," she said.
"Eating wild mushrooms is just not worth the risk. Don't eat mushrooms you have found in the wild, and only purchase mushrooms from a reputable supplier."
The ACT government undertakes routine site inspections at known, high yielding sites on a weekly basis between February and June.
Death cap mushrooms were on Friday detected around Canberra and removed.
The deadly mushrooms often grow near established oak trees and can easily be mistaken for edible mushrooms.
Wild mushrooms should not be touched with bare hands, and children and animals should be kept away from them.
Anyone who finds mushrooms in their yard should wear disposable gloves to remove and dispose of them.
People should urgently attend an emergency department if they believe they've eaten a wild mushroom.
They should also take any remaining mushroom to the hospital for identification.
Symptoms of poisoning generally occur 6 to 24 hours after eating mushrooms, and include pains, nausea, vomiting and diarrhoea.
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