Generate a question that has the following answer: Stu is Stephen's son for the following movie plot: Stephen, a shell-shocked Vietnam veteran, returns from a mental hospital, which he entered voluntarily because he was suffering from nightmares about the war and had in consequence lost three jobs in a row. After having been treated and finally coming home again, he gets a new job as custodial engineer at a grammar school, but loses it again within less than one week because of a law forbidding people who spent time in a mental hospital to work within the vicinity of children. However, the Simmons family desperately needs money, so Stephen continues looking for work, and finds a job picking potatoes. There he makes friends with a man called Moe Henry, with whose help he succeeds in obtaining a job working in a mine - his best one yet. In the meantime, the twins Lidia and Stu try to get away from the dreary reality of their lives. They find a tree in a forest close to their house and decide to build a tree house there. At first they and their friends argue over who has to construct it and who is allowed to use it; the three boys - Stu, Chet and Marsh - want it all to themselves, while the girls - Lidia, Elvadine and Amber - want them to work on it and share it afterwards. After several deals, they agree to build the tree house together. The girls get everything they need from the garbage heap belonging to the Lipnickis, a neighboring family with a reputation for bullying, who have a grudge against the Simmons and their friends. Unfortunately Billy, the youngest of the Lipnicki kids, discovers Lidia, Elvadine and Amber on his father's territory, so the girls have to pay him to keep quiet, but later after he falls under a candy coma his brothers force him to betray Lidia's secret. While the children are busy building their tree house, Stephen and Moe are caught in a collapse as they drain water out of a cavern. Moe is caught under falling rubble, but Stephen, who in Vietnam had to leave his best friend to die in order to be rescued himself, is determined to save him, even if it costs him his own life. He frees...
A:
How are Stu and Stephen related in the movie?