  Rotation Powered-Pulsars are subjected to long-term changes in their period
of rotation, which are measured by timing observations of their rotation
frequency and its derivatives ($\Omega$, $\dot{\Omega}$, $\ddot{\Omega}$). If
the spin-down is solely due to dipolar radiation, the braking index should be
$n=3$. To date, only a handful of braking indices have been estimated for young
pulsars, and in all cases one observes that $n<3$. These observations suggest
that there are complex spin-down processes taking place in the pulsar that are
not fully well understood. In the present work we revisit the spin-down of
young pulsars by considering a possible magnetic field growth due ohmic
diffusion. In order to perform such study we perform calculations with
phenomenological growth functions for the magnetic field. With that we are able
to calculate the spin evolution of the neutron star with all relevant
quantities. We show that such approach could explain the low values of $n$ in
very young neutron stars and may be relevant to explain why a small group of
neutron stars (including central compact objects) exhibit no evidence of a
standard magnetic field. We find that the possibility of magnetic field growth
are relevant to the spin evolution of young neutron stars, and therefore should
not be neglected.
