At the wedding reception of Lou Pickles and his new wife, Lulu, mother-child dance during the reception saddens Chuckie Finster, who realizes that he has lived over two years of his life without his mother, who died of a terminal illness shortly after he was born. His father, Chas, shares Chuckie’s loneliness.
Tommy Pickles’ father, Stu, is summoned to EuroReptarland, a Japanese amusement park in Paris, France, to fix a malfunctioning Reptar robot. Due to Stu being called in the early morning thanks to the time difference, he ultimately brings Tommy, Chuckie, Phil, Lil, Angelica, Dil, their dog Spike, and their parents to Paris to take a vacation at the park.
Coco LaBouche, the head of EuroReptarland, plans to succeed Mr. Yamaguchi as the president of the entire Reptar franchise and its parent company, Yamaguchi Industries, upon his retirement. Yamaguchi says that his successor has to love children to be able to do the job, so Coco tricks him into thinking that she is engaged to a man with a child. Upon the Rugrats’ arrival at EuroReptarland, Angelica overhears a conversation between Coco and Yamaguchi before being caught. To save herself, Angelica reveals that Chas is looking for a wife and suggests that Coco marry him.
Coco strikes up a relationship with Chas, but her attempts to bond with Chuckie fail. The adults and babies meet Coco’s overworked assistant Kira Watanabe and her daughter, Kimi, who hail from Japan, but are now living in France. Kira helps LaBouche to win Chas’ affections. Meanwhile, Spike gets lost in the streets of Paris and falls in love with a stray poodle named Fifi.
Kira tells the babies the origins of Reptar, explaining he was a feared monster until a princess revealed his gentler side to make the frightened humans like him. Chuckie decides the princess should be his new mother, and is aided by his friends to reach an animatronic replica of the princess in the park, but they are stopped by Coco’s ninja security guards. At the show’s premiere, Angelica informs Coco of Chuckie’s wish, so Coco sneaks backstage and takes the spotlight as the princess, luring Chuckie into her arms to make her seem wonderful with children. Chas is ecstatic, deciding she would make an excellent mother and decides on the spot to marry her.
On her wedding day, Coco, along with her accomplice Jean-Claude, kidnaps the children and traps them in a warehouse, including Angelica. Kira attempts to tell Chas the truth, but Coco throws her out of her limo. Chuckie rallies the children to crash his father’s wedding at Notre Dame de Paris using the Reptar robot. They are chased by Jean-Claude, who pilots Reptar’s nemesis, the Robosnail robot. The chase culminates in a fight on a bridge, and Chuckie knocks Robosnail into the Seine River.
Chuckie interrupts the wedding and Jean-Claude reveals Coco’s true nature by announcing that her kidnapping plot had failed, reveals that she had locked the babies up to prevent them from coming. Chas, finally seeing Coco for the wicked liar she really is, angrily calls the wedding off. Angelica also reveals Coco’s true nature to Yamaguchi, who is also in attendance, and the former president dismisses Coco from EuroReptarland. Angelica rips Coco’s wedding dress and Coco runs out of the church humiliated and defeated and Spike chases Jean-Claude away. Kira arrives at the church and apologizes to Chas for what Coco did to him and Chuckie. Chas and Kira eventually marry upon returning to the United States. Spike’s new girlfriend, Fifi, is adopted by the Finster family. Chuckie gets Kira as a new mother, and Kimi as a new sister.