Someone keeps leaving toys at my son’s grave

Dear Delyara, My son died six years ago at the age of eight. For the past three months, someone has been leaving small toy cars at his grave. Different colours, always new, placed beside the headstone. Nobody in the family knows who it is. The cemetery has no camera facing that section. At first, I felt grateful. Then fear entered. Did this person know my son? Did he have a friendship we never heard about? Is it an adult carrying guilt? A child who remembers him? Someone confusing the grave with another? Yesterday, there was a red car identical to the one my son held in his final school photograph. I sat beside the grave for two hours hoping the person would return. Nobody did. My husband thinks we should leave the mystery alone and accept the kindness. I cannot. Grief has already left me with too many unanswered questions. Now every toy feels like a message written in a language only the sender understands.