  Recent observations of the magnetic field in pre-main sequence stars suggest
that the magnetic field topology changes as a function of age. The presence of
a tachocline could be an important factor in the development of magnetic field
with higher multipolar modes. In this work we performed MHD simulations using
the EULAG-MHD code to study the magnetic field generation and evolution in
models that mimic stars at two evolutionary stages. The stratification for both
stellar phases was computed by fitting stellar structure profiles obtained with
the ATON stellar evolution code. The first stage is at $1.1 \mathrm{Myr}$, when
the star is completely convective. The second stage is at $14 \mathrm{Myrs}$,
when the star is partly convective, with a radiative core developed up to
$30\%$ of the stellar radius. In this proceedings we present a preliminary
analysis of the resulting mean-flows and magnetic field. The mean-flow analysis
shown that the star rotate almost rigidly on the fully convective phase,
whereas at the partially convective phase there is differential rotation with
conical contours of iso-rotation. As for the mean magnetic field both
simulations show similarities with respect to the field evolution. However, the
topology of the magnetic field is different.
