Hmm, tough one. The immediate, instinctive answer is stop and help and explain what happened when you got to school.
However, if you are at the point of being suspended for lateness then there is clearly and extensive track record and a whole raft of excuses for lateness have gone before. The teachers are unlikely to take the legitimate reason on board, a classic case of 'the boy who cried wolf'.
As the injuries are relatively minor I think I would continue on my way to school and tell them that there is an injured child near by.