The child would be taken to the hospital in the ambulance in most circumstances. If the EMS (in consultation with the emergency room doctors) declared him dead at the scene, his body would be covered with a tarp or a sheet and would remain there until someone from the medical examiner's office arrived to investigate.
Either way, after triple-checking the identity of the child, the police would send at least two people (possibly including a chaplain, if available) to the house to notify the family.
Cogito ergo summopere periculosus.
Fiat justitia, ruat coelum.