某一天,宇宙人西里里来到小新家中,并使用特使光线把变爸爸野原广志 和妈妈野原美伢回了小孩子模样,如果想恢复现状,必须帮助西里里找回自己的父亲,就这样大家踏上了寻找之旅……One day, the Nohara family met a mysterious alien from outer space named Shiriri. On being basked by a ray emitted by Shiriri, Hiroshi and Misae became 25 years younger and appeared as kids. To be able to return back into adult form, they must find Shiriri's father, who is somewhere in Japan. This situation, which initially started with Shinnosuke's family and later his friends, gradually involves the entire of Japan.