That's not a 'run of the mill' offence, so it's hard to compare it with anything similar. Here's the document judges are obliged to refer to:
http://www.sentencing...inst-the%20person.pdf
It's the table on page 17 which is relevant. However the sentences there refer to a first-time offender convicted of a single offence after a trial. Your guilty plea can get a third knocked off those sentences but the multiple offences (and the fact that the victims were minors) will push the sentencing higher.
I'd guess at a sentence of around 2½ to 3 years imprisonment, of which half will actually be spent 'inside'.
Chris