  Neutron stars (NSs) play essential roles in modern astrophysics. Magnetic
fields and spin periods of newborn (zero age) NSs have large impact on the
further evolution of NSs, which are however poorly explored in observation due
to the difficulty of finding newborn NSs. In this work, we aim to infer the
magnetic fields and spin periods (Bi and Pi) of zero-age NSs from the observed
properties of NS population. We select non-accretion NSs (NANSs) whose
evolution is solely determined by magnetic dipole radiation. We find that both
Bi and Pi can be described by log-normal distribution and the fitting
sensitively depends on our parameters.
