I still don't get it, I'm afraid.
There are degrees of tears, as there are laughter. Brief eye-watering or a trembling lip isn't quite the same as "taking to your bed and sobbing" and to be honest, if someone is doing this over a 5 year old's comments I would be highly surprised if there wasn't something more at work (e.g. depression).
There are cultures where people cry and wail for days when a family member dies and will sit and cry with anyone who loses someone. It is completely acceptable and even expected. In Ireland, if someone dies tragically, the whole church will cry with the bereaved. From discussions with friends/colleagues etc, that would be considered terribly unseemly and out of control in some circles here and even crying at your own parents' funerals is not necessarily the norm. In the past, living would have been very harsh in some places in Ireland e.g. the islands etc but "keening" at funerals and American wakes was part of the tradition. From my understanding of my grandparent's generation, say, if a woman had cried at something trivial in the home no one would have batted an eyelid but it was different for men (unless they were singing songs and sobbing into their pints, which was also generally part of the culture). To me, that says a lot about how crying is seen as weak as associated with women etc.
I thinkm personaly, whether tears are over serious or trivial things is neither here nor there: it's what they mean in the context of the person and the situation and how you would generally construe their actions etc. And yes, of course in some situations, tears might be seen as "weak" and perhaps sometimes they are. However, that is both individually and socially constructed. I remember seeing my grandfather (mother's father) shed a tear at the Sound of Music when I was 10 or 11. I couldn't understand it because it seemed pretty boring to me but if it made me change my opinion of him it was in a good way. He was usually a terribly stern man, prone to being "vexed" at children's behaviour (and then woe betide you!) so in some respects, it was good to see another side, some softness. In later years, I realised that the reason he had shed this tear (in a very refined way, I might add) was not because of the film, but because his twin sister had just been diagnosed with end-stage cancer (unbeknownst to me at the time). That added a poignancy to my memory, but it didn't transform it from one of disgust at his soppy weakness to understanding as it was something worthy of tears iyswim.