  We have discovered kiloparsec-scale extended radio emission in three
narrow-line Seyfert 1 galaxies (NLS1s) in sub-arcsecond resolution 9 GHz images
from the Karl G. Jansky Very Large Array (VLA). We find all sources show
two-sided, mildly core-dominated jet structures with diffuse lobes dominated by
termination hotspots. These span 20-70 kpc with morphologies reminiscent of FR
II radio galaxies, while the extended radio luminosities are intermediate
between FR I and FR II sources. In two cases the structure is linear, while a
$45^{\circ}$ bend is apparent in the third. Very Long Baseline Array images at
7.6 GHz reveal parsec-scale jet structures, in two cases with extended
structure aligned with the inner regions of the kiloparsec-scale jets. Based on
this alignment, the ratio of the radio core luminosity to the optical
luminosity, the jet/counter-jet intensity and extension length ratios, and
moderate core brightness temperatures ($\lesssim10^{10}$ K), we conclude these
jets are mildly relativistic ($\beta\lesssim0.3$, $\delta\sim1$-$1.5$) and
aligned at moderately small angles to the line of sight (10-15$^{\circ}$). The
derived kinematic ages of $\sim10^6$-$10^7$ y are much younger than radio
galaxies but comparable to other NLS1s. Our results increase the number of
radio-loud NLS1s with known kiloparsec-scale extensions from seven to ten and
suggest that such extended emission may be common, at least among the brightest
of these sources.
