I had previously listened to Amira Willighagen as well as Patrícia Janečková. These young singers are phenomenal and each year brings (or will bring) more depth and body to their voices.
For me, it started with Jackie Evancho, and I have to agree with other comments I have read that Jackie's purity and pitch are unparalleled. Amira sings with more vibrato, but constant vibrato (which for some reason seems to be well received in the operatic world) is actually what has kept me at some distance from the genre, and like many things that have interest through contrast, the contrast between a pure non-modulated voice carefully transitioning in and out of vibrato is the most pleasing and interesting to my ears.
Here is an interesting video that composites Jackie Evancho singing
O Mio Babino Caro through the years from age 8 at home to age 10 at her America's Got Talent debut to age 14.
https://www.youtube.com/watch?v=FE_EWoI1Fx4Steve