The forensic investigator allegedly molested two girls aged seven and eight on Monday when he visited their school to prepare pupils for a court appearance.
"A person entrusted with protecting children has violated their trust, " Lesufi said in a statement.
"The children have now become victims of sexual assault twice."
The opposition Democratic Alliance party called for better vetting, saying that 57 police officers with criminal records are employed in units specialising in child protection.
More than 100 rapes are reported to police every day in South Africa, and police are often accused of inadequately investigating alleged assaults and failing to treat victims properly.