A former school headteacher set up a false Facebook account to befriend two 11-year-old Derbyshire girls online and then asked them to take their tops off for him.
David Warbrick set up the online profile and initially began chatting to the youngsters, who are both from Ilkeston, before asking them to go on a webcam and take their tops off, Derbyshire police said.
But police were called after the mother of one of the victims discovered the online web chat conversation.
They arrested and charged Warbrick, 51, with two counts of causing the underage girls to engage in online sexual activity, which he pleaded guilty to at Derby Crown Court this week.
A Derbyshire police spokesman said: “The offences took place in August 2013.
“Mr Warbrick created a false Facebook identity and contact the two girls, who were 11 at the time and were from Ilkeston.
“He began chatting to them on Facebook at first and then invited them to a web chat. He told the girls his camera was not working so they were unable to see him but he could see them.
The BBC have reported how Warbrick, of St Giles Road, Lightcliffe, Halifax, was suspended as head of All Saints Junior and Infants School, in Halifax, and Gomersal Primary School, Cleckheaton, after his arrest in 2015.
The police spokesman said: “The mother of one of the 11-year-old girls came across the web chat between her daughter and Mr Warbrick.
“She contacted the Child Exploitation and Online Protection Centre, which referred the matter to us.
“Our investigations included computer analysis which led us to Mr Warbrick and we asked officers from West Yorkshire Police to attend his address where they arrested him.
“Our officers then travelled to Halifax police station where they questioned him about the girls’ mother’s allegations.”
A spokesman for Kirklees Council, in West Yorkshire, said: “We can confirm that David Warbrick was suspended from his headteacher post as soon as these allegations came to light some time ago.
“He did not return to school prior to leaving his post permanently in 2015.
The sentencing of Warbrick was adjourned until June 13.