  We report on the JVLA observations of three high redshift Active Galactic
Nuclei (AGN), having a black hole mass estimated to be among the largest known.
Two of them, SDSS J0100+2802 and SDSS J0306+1853 at redshift 6.326 and 5.363
respectively, are radio-quiet AGN according to the classic definition, while
the third (B2 1023+25 at z=5.284) is a powerful blazar. The JVLA data clearly
show a radio structure in the first source, and a radio emission with a
relatively steep radio spectrum in the second one, demonstrating the presence
of a radio jet and a diffuse component. Therefore, being radio-quiet does not
exclude the presence of a powerful relativistic jet with important consequences
on the population studies and on the ratio between jetted and non-jetted AGN.
We can estimate the viewing angle of these jets, and this allows us to find,
albeit with some uncertainty, the density of black holes with a mass in excess
of $10^{10}M_\odot$ at high redshifts. We found that their density in jetted
AGN is very large in the redshift bin 5-6, comparable with the overall AGN
population of the same optical luminosity. Jets might thus play a crucial role
in the fast formation and evolution of the most massive black holes in the
early Universe. They are more common than what expected from wide radio surveys
with mJy flux sensitivity. Deeper JVLA or VLBI observations are key to discover
a possible relativistic jet population hiding in plain sight at very
high-redshift. The discovery of powerful relativistic jets associated with the
most massive black holes in the early Universe re-opens the question: is the
jet instrumental for a rapid growth of the black hole or instead is the black
hole mass the main driver for the jet formation?
