*, [child parentFilter=docType:"VEHICLE" childFilter="promotion.startDate_dt:[2018-04-03T00:00:00Z TO ] AND promotion.endDate_dt:[ TO 2018-04-03T23:00:00Z]"]

Or Try

*, [child parentFilter=docType:"VEHICLE" childFilter="startDate_dt:[2018-04-03T00:00:00Z TO ] AND endDate_dt:[ TO 2018-04-03T23:00:00Z]"]

Add double quotes in childFilter value, it should work.