Is a child allowed to lie or sleep in a parent’s bed?
It is permitted for a child to sleep in his parent’s bed.
The Gemara in Kiddushin (31b) cites from a baraisa that it is forbidden for a child to sit in his father’s place, or to stand in his fixed place.
Rashi explains that this refers to a “place where his father stands among the elders for advice” (see also Ran 13a). The implication is that the prohibition refers to a place of honor, such as the top of the table, and so on. However, for a place that involves no special honor of a father, no prohibition will apply to the son’s sitting there.
The Tur (Yoreh De’ah 240) cites the interpretation of Rashi, and adds, in the name of the Rama, that the same applies to a place which is special for the father to sit. The Beis Yosef explains that there is no dispute in this matter. For our purposes, it is possible that both agree that the prohibition is limited to a seat or place that involves a parent’s honor.
A source for this idea is found in the Aruch Hashulchan (240:9), who makes special mention of the “head of the table,” implying that the prohibition refers to matters of honor, and not to a simple place where the father sits, which does not involve any honor.
This ruling is given by the sefer Mora Horim U-Kvodam (p. 29, no. 20), in the name of Rav Elyashiv shlita and others. The sefer writes that “It is permitted for a son to sit or sleep in his father’s bed, even in the father’s presence,” the footnote explaining that the prohibiton refers only to a place of honor, and not to places that do not involve honor, such as a bed.
Note that when the parent (and other relatives) is not present, there is still greater room for leniency, as the Ben Ish Chaim (Shoftim 2:2) writes.