You may find our discussion guide published last year, a generic framework for discussing a terrorist attack, helpful in structuring and safely facilitating such discussions with pupils. 
We have also produced a series of four lesson plans on preventing extremism for key stage 4 (in partnership with Medway Public Health Directorate) which members can download and incorporate into their schemes of work for PSHE education, which can be found here
Our thoughts are with everyone affected in any way by yesterday's tragic incident and thank you for the work you continue to do to support children and young people in difficult times.