You need have 肝损伤 proof to claim damage. You should complain to

& tell them what has happened and be prepared for further action.  Generally speaking, based on drug pharmacology,  I don't think you need to worry too much as a 6+ kid can tolorate in a short period an adult drug dosage like your case, a doubling dosage.  Definitely overdosing should be avoided, if possible, especially for a long time usage.