does anybody have any hints?

Thank you

A sound technique that gets guided by a teacher and slowly it will begin to appear on its own accord.

That's it really. If a young voice has a natural vibrato, and I really do mean a totally natural one, then there is usually nothing to be done. If it does not then make sure that the technique is coming on in the right way and that no strange habits are creeping in and it will appear eventually. It is rare for a voice that is trained to have no natural vibrato but there is plenty of good repertoire to be found for one that does not. The time to worry is when a pupil has a rapid throat vibrato or an artificial one that is being forced.

That was very well put Petra.

Isn't it nice when singers have "Wow! That was ME!" moments.

Those moments are wonderful aren't they? But they're also scary in a funny sort of way, because you never look back.