Please let me know if there is a reason why a child can have bad breath?

Child's bad breath: Child's bad breath could be caused by sinusitis, post nasal drip, GI problems, inadequate oral hygiene, candidiasis and a host of other conditions. See a pedodontist and pediatrician for an evaluation.

Lots of reasons: Most often in children bad breath from infected teeth/gums, especially if teeth are not being flossed daily, or from infected tonsils. Please have your dentist/pediatric dentist and your physician/pediatrician take a look and advise you.