IMO, smoking marijuana in the privacy of one's own home should not be a crime. Smoking marijuana in a closed vehicle with a child should be a crime, but still not punishable by death. However, it does show a reckless disregard for others. Someone who would force a 4-year-old to get a contact high and also drive around under the influence with a child in the car would probably not be incredibly cooperative during a traffic stop. The bottom line is, I don't have enough information at this time to say whether the shooting was justified or not.
I do not drink so don't know. Can you drink in a car if no one is driving at the time? Don't know if it is true anymore, but in Louisiana they had drive in's where you could get a drink. The driver could not be drinking but everyone else could.
In MN, you cannot have an open bottle in a car, but is that only while moving?