You should take them to a doctor immediately. Inform the doctor about the mold exposure, as this is a critical piece of information for diagnosis. The pediatrician can assess if the cough is an allergic reaction or a more significant mycotoxin exposure and recommend appropriate treatment. In parallel, you must address the source. The AC leak is the root cause; simply cleaning the wall is insufficient. A professional inspection is necessary to identify the extent of the leak, the spread of mold inside the wall cavity, and the specific species present through lab testing. Remediation must fix the moisture source, contain the area to prevent spore spread during cleaning, and properly dispose of contaminated materials like drywall or insulation. Until it’s professionally handled, keep the children out of that room and ensure good ventilation throughout the apartment.