You need a lawyer if you do not have one already. This is a job for a professional. Please do not
try to handle this mess yourselves.
Talk to him or her about disproving these kinds of charges. E. g. do you need an investigator to come to your house, do you need expert testimony from a pediatrician, something else? Yes, this is going to cost you some money. But it's better than either of you being falsely labeled as sex offenders as collateral damage from this vendetta.