The $\gamma$-ray detection from several radio-loud (RL) narrow-line Seyfert 1 (NLS1) galaxies has enabled us to study powerful relativistic jets in active galactic nuclei (AGNs) with smaller black hole masses and higher accretion rates than classical blazars. However, the sample of those $\gamma$-ray detected NLS1s available is still not large enough for a comprehensive and statistical study. We provide a summary of our detections and follow-up studies of three $\gamma$-ray-emitting NLS1s: SDSS J211852.96$-$073227.5 with flaring $\gamma$-ray radiation (Yang et al. 2018, Paliya et al. 2018) and SDSS J122222.55$+$041315.7 with the highest redshift by far (z$\sim1$) (Yao et al. 2015a), along with the prototype 1H 0323$+$342 (Zhou et al. 2007, Yao et al. 2015b). And we will discuss their multiwavelength properties and variability properties, including implications from high-energy observations in $\gamma$-rays and X-rays, infrared and radio properties, and correlated variability between several wavebands.