Between 1974 and when? Given a ten year span for that figure (74 to 84) that puts the risk at less than 1 in 30 million per child per year. SInce you can only be a child for about 15 years, that means the risk per individual is around
1 in 2 million, which is well below my threshold for alarming risks.If you make a set of assumptions designed to justify the detectors, (the detectors prevent 75% of such accidents, somewhere in the vicinity of 8 million relevent garage doors in the country), you could expect, at best, a 1/125,000 chance that any given installation will prevent an accident.
If the things add $20 to the cost of the door, then it makes sense to add them if you can't save more than one life by spending 2.5 million dollars somewhere else.