<qa>  What is the maximum age of children with severe TBI?Specific Aim: Define the capacity of the combination of probenecid and NAC to safely and synergistically preserve levels of GSH and reduce oxidative stress in children with severe TBI. We will enroll 20 children age 2 to less than 18 years old less than 216 months after severe TBI in a randomized, controlled study of administration of the combinational therapy and test if the administration of these drugs is safe and if antioxidant reserve can be preserved within the serum and CSF. 