  We present VLT/SINFONI J, H+K spectra of seven close visual pairs in M dwarf
binary/triple systems, discovered or observed by the AstraLux M dwarf survey.
We determine the spectral types to within 1.0 subclasses from comparison to
template spectra and the strength of K-band water absorption, and derive
effective temperatures. The results are compared to optical spectral types of
the unresolved binary/multiple systems, and we confirm that our photometric
method to derive spectral types in the AstraLux M dwarf survey is accurate. We
look for signs of youth such as chromospheric activity and low surface gravity,
and find an age in the range 0.25-1 Gyr for the GJ 852 system. Strong Li
absorption is detected in optical spectra of the triple system J024902 obtained
with FEROS at the ESO-MPG 2.2m telescope. The equivalent width of the
absorption suggests an age consistent with the beta Pic moving group. However,
further observations are needed to establish group membership. Ongoing orbital
monitoring will provide dynamical masses and thus calibration of evolutionary
models for low mass stars.
