In the constructivist structure, a child is viewed as–

The constructivist approach is based on the idea that meaningful learning takes place when learners actively construct their knowledge.

• The central idea of the constructivist frame is that learners learn through experiencing things and reflecting on those experiences.

Key Points Central ideas of the constructivist frame:

• Children are active explorers or problem solvers of the environment. 
• Children are little scientists and markers of meaning.
• Children are builders and creators of new knowledge.
• Children are born to be like 'scientific investigators' and 'problem solvers'.
• Children’s thinking is qualitatively different from that of adults not quantitatively.
• Children learn through experiencing things and reflecting on those experiences.
• Children are born to construct the meaning of their environment through social interaction.

Thus by all these references, we can consider that, In the constructivist structure, the child is viewed as a problem solver and a scientific investigator.