Final answer:
In the preoperational stage, between 2 and 7 years old, children use substitutes to represent objects they do not have, engaging in pretend play using symbols.
Step-by-step explanation:
The stage of material use where kids find substitutes to represent objects they do not have is known as the preoperational stage, which occurs approximately from 2 to 7 years old. During this stage, as theorized by Jean Piaget, children begin to engage in symbolic play and pretend play. For instance, they might use a stick as a substitute for a sword or pretend their arms are airplane wings. This represents a significant development in a child's cognitive abilities where they start to use symbols and engage in creative substitute use for objects that aren’t available to them.
Children’s logic in the preoperational stage is strongly influenced by their personal experiences. Despite their ability to use symbols, they cannot yet perform mental operations like understanding conservation – the idea that quantity or volume does not change with transformation in shape or appearance. Hence, a child at this stage might actually believe that a slice of pizza cut into more pieces is more than an uncut slice of the same size.