Using the false-belief task, researchers find that children under age are not likely to have developed a "theory of mind."

Under age of three (3)

Explanation:

The theory of Mind is a cognitive skill which is related o understanding the minds of the other person and their own that is how the other person will act or why the person acts in this way.

The theory of mind is based on the belief, intention and desire and emotions and analysing those attributes to understand the minds of the other person.

The task used to measure the Theory of mind is known as a false brief task which when performed on the children under ages gave incorrect answers.

But when the test was performed on children's above 4 years the children's stared giving the correct answer.

Thus, under the age of three is the correct answer.

4

Explanation:

The theory of mind suggests that children grow with different perspective at different age as they attain awareness with their surrounding environment.

The child of 4 years will likely to distinguish between what has been told to him or her and what's true in reality. Thus the false believes may dimnish in this age due to cognitive development.