The purpose of this study is to describe the pharmacokinetics of moxifloxacin in children to see what the best dose should be for children in the future. Pharmacokinetics is to see how the body absorbs, distributes, breaks down and gets rid of the study drug. The pharmacokinetics of certain drugs may be altered in children due to developmental differences in various organ functions responsible for drug elimination, as well as in general distribution characteristics. The safety of moxifloxacin in children with infections will also be looked at. Results from this study will be used to guide dosing strategies of the larger clinical trial planned for children