  Supernova remnants (SNRs), star formation regions (SFRs), and pulsar wind
nebulae (PWNe) are prime candidates for Galactic PeVatrons. The nonthermal
high-energy (HE, $\varepsilon>100 \textrm{ MeV}$) and very high-energy (VHE,
$\varepsilon>100 \textrm{ GeV}$) $\gamma$-ray emission from these sources
should be a promising manifestation of acceleration processes. We investigate
the possibility to explain the HE and VHE $\gamma$-ray emission from the sky
region of the magnetar SGR 1900+14 as a signature of cosmic rays accelerated in
above mentioned sources. To this end, we simulate the $\gamma$-ray emission
from the extended Fermi-LAT HE source 4FGL J1908.6+0915e, the extended VHE
H.E.S.S. source candidate HOTS J1907+091, and the point-like HAWC TeV source
3HWC J1907+085, which are spatially coincident with the SNR G42.8+0.6, the
magnetar SGR 1900+14 and the star forming region W49A. The simulations are
performed within the hadronic and leptonic models. We show that the observed
$\gamma$-ray emission from the region of the magnetar SGR 1900+14 can, in
principle, include contributions of different intensities from all three types
of (potentially confused) sources. The considered in detail cases of a
magnetar-connected but still undetected SNR and a PWN are the most promising
ones, but with a serious requirement on the energy reserve of radiated CR
particles - of order of $10^{51}d_{\textrm{10kpc}}^{2}$ erg for sources at a
distance of $d\sim 10$ kpc. Such energy reserve can be provided by the
magnetar-related Hypernova and/or magnetar wind nebula remnant created by the
newborn millisecond magnetar with the large supply of rotational energy
$E_{\textrm{rot}}\sim 10^{52}\textrm{ erg}$.
