Final answer:
The term for the problem when a child says 'b' when shown both a 'b' and a 'p' is overgeneralization. It is a common occurrence in language development.
Step-by-step explanation:
The term for the problem described, when a child says 'b' when shown both a 'b' and a 'p', is overgeneralization. Overgeneralization occurs when a language rule is extended to exceptions to the rule. In this case, the child is generalizing the rule that 'b' represents the sound [b] to include the letter 'p', which is an exception to the rule. This is a common occurrence in language development as children are learning and applying language rules.