Resources for Moed Katan 26
1. The גמרא says that we tear קריעה when seeing the מקום המקדש as well as when seeing ערי יהודה וירושלים בחורבנן. The question is what is the status of these places today? Are they still considered בחורבנן? See the אגרות משה in או"ח חלק ד סימן ע' ס"ק י"א who says that any place (other than the מקום המקדש) where the Jews rule over does not need קריעה. Therefore, he says that one would not tear קריעה when seeing any part of Israel that is part of the state of Israel. However, any part of ערי יהודה וירושלים that is not under Jewish control would still require קריעה even if Jews live there. See the עקבי הצאן in סימן י"ח who quotes Rav Soloveitchik ז"ל who held that the קדושה of ירושלים came from the מקום המקדש itself and that even if ירושלים was under Jewish rule it would still require קריעה, unlike ערי יהודה which would not require קריעה if under Jewish rule. See also the שו”ת מנחת שלמה ח”א סוף סי’ עג who says that as long as we do not have the ability למעקר פּולחנא נוכראה from ירושלים, it is still called בחורבנה. Therefore, one must still tear קריעה nowadays.
2. The גמרא says that if someone is sick and will become sicker if you tell them that a close relative of theirs died, then you should not tell them. The simple משמעות of this is that if the person is a regular healthy person, you ought to tell them about the passing of their relative. See the ר"ן here who makes this דיוק and says that while it isn’t מוכרח in the גמרא it makes sense that you must to tell the person so that they don’t do things that an אבל can’t do. However, see the שולחן ערוך in סימן ת"ב סעיף י"ב who says that one never needs to tell someone that they lost a relative. Even the רמ"א there only disagrees by sons since they need to say Kaddish for their parents. Moreover, the מחבר brings from רש"י that one is even allowed to invite the person to a wedding! See also the פּתחי תשובה in אות ב who brings the פּנים מאירות who says that on פּורים and חול המועד you aren’t even allowed to tell the אבל! As to why this is true, if אבילות is only דרבנן it is easier to understand as there is a famous נתיבות (in חו"מ סימן רל"ד ס"ק ג) that says an איסור דרבנן בשוגג is מותר. Similarly, the ש"ך in סימן שע"ב ס"ק ג says that if a כהן is sleeping and then someone dies nearby, you only need to wake him up if there is טומאה דאורייתא but not טומאה דרבנן. (It would still seem difficult to allow someone to invite this person to a wedding based on this.) However, if you hold that אבילות on the first day is דאורייתא, then one must say as the שבלי הלקט says in הל' שמחות סימן מ"ז that דיני אבילות don’t begin at all until the person is aware of the death and feels sad.
3. The גמרא says that we make a child tear קריעה because of עגמת נפש (to make others sad). There is a מחלוקת ראשונים whether this גמרא is even referring to a child who was הגיע לחינוך. The רי"ץ גיאות is quoted by many of the ראשונים as saying that our גמרא is only talking about a child who hasn’t reached the age of חינוך, but if he had reached that age then he would be חייב in קריעה because of חינוך. According to that, an eight year old child should be חייב in all דיני אבילות, not just קריעה. However, see רש"י in תענית דף י"ג: ד"ה אין הבוגרת who says that there is no חיוב אבילות at all for children. See the חכמת אדם in כלל קנ"ב סעיף י"ז who says that even though it is a מחלוקת הפּוסקים, the מנהג is that we don’t do חינוך for דיני אבילות. The reason is that since it is a דבר של צער they were never גוזר, just like we don’t find a חיוב אבילות for children on תשעה באב.