How can Kuang Tianyou and Ma Xiaoling have children?

Two people gave each other. In the TV series, I have an agreement with zombies. In the plot, Kuang Tianyou and Ma Xiaoling fall in love and give themselves to each other. Ma Xiaoling was pregnant and gave birth to a child. I have a Date with Zombies is a fashion fantasy TV series produced by Hong Kong ATV, produced by Tian Liang and Zhiwei Xian, starring Yin Tianzhao, Joey Meng Yee Man Iman, Chen Qitai and Kristy Yang.