My son rode the bus to K last year. We had no problems -- although we put him on the bus in the morning and most days he went to aftercare in the afternoon
Something I did (and will do again this year) put my name, phone number, address, etc on a tag on his backpack. Let him know it was there. if he got lost/needed me called, he'd have all the information at his fingertips and not have to rely on remembering it.