Actually , there are not many really talanted children on youtube.
Quite a few of them are over-trained and over-precessed playing pieces way beyond their understanding. Just because they them can play lots of notes very fast does not make them into good musicians.
I really would not go by grades - they just dont mean anything except the fact the child hase been trained to play 3 pieces and certain scales.
A lot of naturally bright kids wizz through early grades - this is just the beginning.
I heard a 13 yo boy playing some diploma standard pieces on piano recently - he has 3 G8s and a G6 on 4-th instrument.
He has done really well and will get scholarships to top schools.He can play in groups and be important part in school's music life.
However he is the most boring piano players who in my opinion will never make it as a pianist as all the magic is missing from the pieces he plays and he enjoys virtiosity for the sake of it. The number of time he has been labled as gifted, talanted etc - I worry about kids like that having to face a reality one day.
I think its really good when parents support music education for their kids, I just would be very careful at labelling a young child as gifted - making of a musician takes years of hard work.