The mother has passed away a while ago, so it's no news for the boy, who obviously remembers her and feels left alone. The singer (nanny, father, stepmother) tells the boy to sleep, so that he has at least the angels for company.

YouTube is full of the most horrible kitsch. There must be decent recordings, but I did not even find an acceptable one. The record companies started the race for maximal reverb and the rock-bottom of taste; that Dutch boy singer runs neck-and-neck with Placido Domingo, Engelbert Humperdinck (the one from India), genuine Tyrolese boys, the daughter of a Romani representative, and many others. That is really sad. Some leave out the verse about the mother, consequentially.