Melatonin is a sleeping drug. These people are giving their babies sleeping pills. And when they turn blue they are bringing them to the ER. It could be babysitters or parents. But melatonin is a pill that does not taste good. A baby would not normally go for this over any other drug.
The melatonin we get is sweet, like with an artificial sweetener. Kind of tasty. Kids would eat by the handful if they could.
There are flavored, chewable melatonin pills.
But child-proofing a home is the absolutely most basic of parental tasks.