Kidnapping
My child was nearly kidnapped

My childs school was contacted by a male person leaving a message that he needs to stay late and not take his normal transport, my son then LUCKILY contacted me to ask why? & I knew nothing of this... turning out that it was a suspicious character. (The school took down no details of the person that called) I have now spoken to the principal about that & they have promised to be more vigilant. I suspect that it was someone he met on BBM, Please I ask that parents check their childrens contacts and if they dont personally know sum1 to delete the contact. The kids are having a compition to see who has the most bbm contacts & therefore they just add anyone... This is very scary as I deleted 40 contacts from his bbm list that he did not know personally, I am unsure what to do to actually trace the person that called but I am going to try opening a case at the police station and see if I can get the CPU involved in tracing the call.
Any suggestions / assistance will be greatly appreciated;