Transient current in transistor-like nanostructures has been studied by a model of a few electrons confined in a one-dimensional effective potential consisting of three quantum wells, 'source', 'gate', and 'drain'. The time-dependent Schrödinger equation for the electrons has been integrated relying on the symplectic integrator method and the transient current has been calculated as the flux of the probability density of electrons absorbed by the complex absorbing potential placed at the far edge of the drain region. The electrons are initially placed in the source domain as their lowest-energy state for a given spin multiplicity and the source-drain current has been calculated for different gate potential heights. The current for different spin configurations has shown strong emission at different values of the gate potential, suggesting use of the studied nanostructures for extracting current with a specific spin configuration from spin-unpolarized normal current. Dependence of the current emission on electron correlation has also been studied by changing the size of the source domain. The current has shown appreciable differences for different spin configurations for the medium and strong confinement regimes, while these differences become smaller for smaller confinement and tend to diminish in the weak limit of confinement. This observed trend has been rationalized on the basis of the formation of the Wigner lattice states.