The Mishna (Eiruvin 86) discusses case where someone plans be away from home for the duration of Shabbos – does that person’s home need to be included them in the local eiruv or not? R’ Shimon says that if a person plans to spend Shabbos by his daughter’s house, even if he will be in the same city, his own house does not need to be included in the eiruv because we assume it will be vacant for all of Shabbos.
The gemara notes that the Mishna speaks specifically of a case where one is visiting one’s daughter – only then can we assume that even if one is not far from home one will remain away as a guest. But if one plans to spend Shabbos with one’s son, that’s a different story – the volatile mix of parents with their son and daughter-in-law leaves little assurance that the entire Shabbos can pass without the parents returning to their own home! All I can say is that Chazal were the keenest observers of the human condition who ever lived.