Explicit memories are those that that we are conscious of: the vivid recollection of a specific event or knowing not only a fact, but also when and where you learned it. The ability to consciously recollect an event or fact doesn't usually fully develop until we are about 6-12 years old.
Implicit memory, on the other hand, describes learning that is unconscious: the repetition of a procedure (such as driving) that becomes a motor memory, or the ability of savvy marketers to keep their products in our minds without our direct awareness. Implicit memory develops much earlier-even infants show signs of unconscious learning.
Therefore, when a child's brain is injured, the age at which they are injured is important to the development of explicit and implicit memories. A recent study has found that children who suffered a brain injury later in their childhood had impaired explicit memory, but preserved implicit memory. Children who suffered a brain injury earlier in their childhood showed impairment in both explicit and implicit memories.
Lah S, Epps, A, Levick W, & Parry L. Implicit and explicit memory outcome in children who have sustained severe traumatic brain injury: Impact of age at injury (preliminary findings). Brain Injury. (December 2010).