Our team is performing an automatic search for very distant sources using HST, VLT, Magellan, Gemini, Spitzer and ALMA dataset around Frontier Fields aiming to study the nature and properties of sources during the epoch of reionization. In this talk, I will present our photometric sample selection, the photometric properties of our z>6 candidates and the evolution of galaxy number densities during the first billion years from a statistical point of view. Thanks to the huge depth of HST FF data, we identified several z>7 candidates selected in previous HST surveys as mid-z interlopers that could bias our conclusions on the evolution of the first galaxies. I will also discuss several interesting objects that will benefit from the arrival of the James Webb Space Telescope. The spectroscopic follow-up has just started, and our team is observing a sample of z>7 sources with some of the most powerful ground-based spectrographs in order to confirm the redshift of these objects and add robust constraints on their physical properties.