  In this article we study the existence of solutions to the system
\begin{equation*}\left\{ \begin{array}{ll} -\left(a+b\int_{\Omega}|\nabla
u|^{2}\right)\Delta u +\phi u= f(x, u) &\text{in }\Omega \hbox{} -\Delta \phi=
u^{2} &\text{in }\Omega \hbox{} u=\phi=0&\text{on }\partial\Omega, \hbox{}
\end{array} \right. \end{equation*} where $\Omega$ is a bounded smooth domain
of $\mathbb{R}^N$ ($N=1,2$ or $3$), $a>0$, $b\geq0$, and
$f:\overline{\Omega}\times \mathbb{R}\to\mathbb{R}$ is a continuous function
which is $3$-superlinear. By using some variants of the mountain pass theorem
established in this paper, we show the existence of three solutions: one
positive, one negative, and one which changes its sign. Furthermore, in case
$f$ is odd with respect to $u$ we obtain an unbounded sequence of sign-changing
solutions.
