Musar for Niddah 32:31

The premature death of minors is connected with the spiritual preparations a husband undergoes before sexual union with his wife. From every such [successful] union a soul is created, i.e. released from G–d's store of souls. If both father and mother at the time of their union were keenly aware of the sacred nature of the commandment they were performing, then the soul released from such emanation by the parents on earth will retain its original state of holiness and purity, if the parents failed to permeate their act of union with an awareness of the holy task they were performing, then that soul may be assigned to Lilith. This is what is meant by Job 3, 3: והלילה אמר הורה גבר, "And 'night' announced a male has been conceived." Our sages in Nidah 16 say that the angel that has been given domain over conceptions is called Laylah; when the parents have not sanctified themselves, however, Lilith oppresses, for the conception originated in the domain of זנונים, gratuitous self-gratification of the flesh. This brings us back to the weak spot in man, i.e. the גיד הנשה.