The purpose of this study is to evaluate blood levels of solifenacin succinate (the study drug) in children with neurogenic detrusor overactivity after taking a single oral dose. If the bladder contracts strongly and without warning, the muscles surrounding the urethra (detrusor muscles) may not be able to keep urine from passing. This may happen as a consequence of spinal cord defects, and then is called neurogenic detrusor overactivity.