  We present a first-look analysis of the JWST ERO data in the SMACS
J0723.3-7327 cluster field. We begin by reporting 10 new spectroscopic
redshifts from $\lambda_\mathrm{obs}=1.8-5.2\mu$m NIRSpec medium-resolution
($R=\lambda/\Delta\lambda = 1000$) data. These are determined via multiple
high-SNR emission line detections, with 5 objects at $1 < z < 3$ displaying
multiple rest-frame near-infrared Hydrogen Paschen lines, and 5 objects at $5 <
z < 9$ displaying rest-frame optical Oxygen and Hydrogen Balmer lines. For the
5 higher-redshift galaxies we extract fluxes in 6 NIRCam bands spanning
$\lambda_\mathrm{obs}=0.8-5\mu$m and perform spectral energy distribution
fitting, in combination with existing HST photometry. The $7 < z < 9$ objects
exhibit a U-shaped pattern across the F277W, F356W and F444W bands, indicating
a Balmer break seen in emission (Balmer jump) and high-equivalent-width
[O\,\textsc{iii}] emission. This indicates an extremely young stellar
population, with the bulk of the current mass having formed within the past 10
Myr. We report robust stellar masses and mean stellar ages from our spectral
fitting, with the four $z > 6$ galaxies exhibiting low stellar masses from
log$_{10}(M_*/$M$_\odot)=7.1-8.2$ and correspondingly young mean stellar ages
of only a few Myr. This work highlights the critical importance of combining
large upcoming NIRCam surveys with NIRSpec follow-up to measure the
spectroscopic redshifts necessary to robustly constrain physical parameters.
