  Based on the systematic Hamiltonian and superfield approaches we construct
the deformed $\mathcal{N}=4,8$ supersymmetric mechanics on K\"ahler manifolds
interacting with constant magnetic field, and study their symmetries. At first
we construct the deformed $\mathcal{N}=4,8$ supersymmetric Landau problem via
minimal coupling of standard (undeformed) $\mathcal{N}=4,8$ supersymmetric free
particle systems on K\"ahler manifold with constant magnetic field. We show
that the initial "flat" supersymmetries are necessarily deformed to $SU(2|1)$
and $SU(4|1)$ supersymmetries, with the magnetic field playing the role of
deformation parameter, and that the resulting systems inherit all the
kinematical symmetries of the initial ones. Then we construct $SU(2|1)$
supersymmetric K\"ahler oscillators and find that they include, as particular
cases, the harmonic oscillator models on complex Euclidian and complex
projective spaces, as well as superintegrable deformations thereof, viz.
$\mathbb{C}^N$-Smorodinsky-Winternitz and $\mathbb{CP}^N$-Rosochatius systems.
We show that the supersymmetric extensions proposed inherit all the kinematical
symmetries of the initial bosonic models. They also inherit, at least in the
case of $\mathbb{C}^N$ systems, hidden (non-kinematical) symmetries. The
superfield formulation of these supersymmetric systems is presented, based on
the worldline $SU(2|1)$ and $SU(4|1)$ superspace formalisms.
