  The escape fraction of Lyman-continuum (LyC) photons ($f_{esc}$) is a key
parameter for determining the sources of cosmic reionization at $z\geq 6$. At
these redshifts, owing to the opacity of the intergalactic medium, the LyC
emission cannot be measured directly. However, LyC leakers during the epoch of
reionization could be identified using indirect indicators that have been
extensively tested at low and intermediate redshifts. These include a high
[OIII]/[OII] flux ratio, high star-formation surface density, and compact
sizes. In this work, we present observations of 29 $4.5 \leq z \leq 8$
gravitationally lensed galaxies in the Abell 2744 cluster field. From a
combined analysis of JWST-NIRSpec and NIRCam data, we accurately derived their
physical and spectroscopic properties: our galaxies have low masses
$(\log(M_\star)\sim 8.5)$, blue UV spectral slopes ($\beta \sim -2.1$), compact
sizes ($r_e \sim 0.3-0.5$ kpc), and high [OIII]/[OII] flux ratios. We confirm
that these properties are similar to those characterizing low-redshift LyC
leakers. Indirectly inferring the fraction of escaping ionizing photons, we
find that more than 80% of our galaxies have predicted $f_{esc}$ values larger
than 0.05, indicating that they would be considered leakers. The average
predicted $f_{esc}$ value of our sample is 0.12, suggesting that similar
galaxies at $z\geq 6$ have provided a substantial contribution to cosmic
reionization.
