\[x - детей;y - конфет.\]
\[\left\{ \begin{matrix} y - 5x = 13\ \ \ \\ y - 8x = - 5\ \ \\ \end{matrix} \right.\ \ ( - )\]
\[\overline{3x = 18}\text{\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ }\]
\[\ \ \ x = 6\]
\[Ответ:6\ детей.\]