Children begin to learn critical thinking when they begin learning language and to encounter difficulties of whatever kind. This begins long before formal education.
The more children of all ages are encouraged, have success, and are rewarded by teachers and parents for using their emerging reasoning skills to address whatever difficulties or problems they may encounter in school and at home, the more the children come to rely on critical thinking.
However, memorization is not the way. Simply following directions without reflection is not the way. Children must be invited to analyze the situation and to propose possible solutions, and to infer and evaluate might then happen next. Simply telling the child the answer is not the way.
It is difficult for parents and teachers to allow children the mental space to exercise their young critical thinking skills. But that space is important, even if small mistakes may occur that will require the children to make corrections. The children need to be asked to explain their own thinking and be guided to reason as well as possible.
The development of core critical thinking skills and mindset in K-12 school children is the foundation of student learning, academic progress and future workplace success. For more information: How to foster critical thinking in children and K-12 students