Explosion sound

May have been a head or intake gasket. When the piston rises in the bore there is a buildup of pressure, when the piston reaches the top of the stroke the spark plug fires and the air fuel mixture combusts driving the piston back down. In your case a gasket may have blew, or the head or block cracked. It may have also been a backfire through the throttle body, although that wouldn't explain the oil pouring out. Needless to say, you had a catastrophic failure of the engine, and it will need to be inspected by a mechanic to assess the damage.

Possible thrown rod. I don't now how engine oil would pour out of an intake manifold.

Sounds like a thrown rod. But I've never heard of an engine throwing a rod while cranking to start it. High engine RPMs are usually involved when an engine throws a rod. If you're getting the story second hand, like from your children, suspect that racing the engine was involved! Hope that helps! Jim