So after they discovered potato chips, they find out the same vendor suddenly started selling fried chicken. Celia realizes that the food must be coming from the reincarnated heroine. They both go on a date into town, disguised as commoners, and come across the restaurant. When they look inside, they see the heroine behind the counter, and the Prince instantly recognizes her as the girl he helped when he was seven years old. He finds himself instantly attracted to the heroine, which Celia noticed. Celia runs away and the prince gets his bearings back and realizes what he's done. He finds Celia and apologizes, wondering if the force of the game made him so befuddled with the heroine. To assert his dedication to Celia, he sneaks her out to the church (with his guard and her maid following in secret) where they say their vows before the goddess. Even though it isn't official, it's still a wedding vow said before witnesses. So now they're "married" at ten years old (lmao).
Celia uses her past life knowledge to begin creating schools for the children, installing baths for orphans, and implementing disinfection procedures using alcohol in the hospitals. At the same time, the heroine is using her knowledge to create more food and creating a burger/fried chicken restaurant. Prince comes across heroine again (at age 11) and realizes that even though he still finds her really cute, he doesn't feel that forceful attraction to her like he did before, so he believes that making the vow to Celia before the goddess must've worked. Doesn't help that heroine immediately knew who the prince was and was being kind of pushy towards him.
Still reading, can't wait until they actually get to the age when the "game" begins.