From the Gabrieli lab, declarative memory pathways require the prefrontal cortex, so no surprisingly, declarative memory pathways take time to fully mature. In this new report, fmri changes develop quite late, with even teens not fully developed as subjects in their 20's.
Interestingly though, medial temporal lobe systems (important for both episodic and declarative memory) were fairly mature by the age of 8.
Developmental studies such as this may be helpful in designing the most efficient ways of using children's memory systems (they may also be helpful in deciding reasonable expectations).
Immaturity of the PFC in children was felt to "limit the episodic specificity of memories such that memories are less likely to be subjectively vivid or objectively detailed."
These are very general conclusions, of course. There are many precocious children with prodigious memories for facts and events, and this may help us understand why these children need differentiation in their educational program. Differences in the right vs. left PFC maturation raises interesting questions about optimizing educational approaches for middle and high school students.
Developmental Changes in Declarative Memory pdf