  Decays $K^{+} \rightarrow \mu^{+}\nu_{\mu} \nu \bar \nu$ and
$K^{+}\rightarrow e^{+}\nu_{e} \nu \bar \nu$ are examined to the leading order
in momenta in the framework of Chiral Perturbation Theory. Predictions of the
Standard Model for the muon and electron differential energy spectra and
branching ratios of $K_{\mu 3 \nu}$ and $K_{e 3 \nu}$ are presented.
