My experience with growing up in a big Mormon family is that being in a "big happy Mormon family" causes too much emotional stress.
In my experience, fighting, crying, and not getting enough emotional support was normal. Pressure to appear as a big happy family all the time is the biggest stress. The amount of suppression it takes to never show negativity is insane. It's unhealthy to expect a big family to be happy all the time like that, but it is unfortunately an expectation in a cult like Mormonism.
I had to take care of the younger kids because young children need so much care and attention, but I was doing this at my own cost because I was still a child who needed time and attention too.
Children deserve to be raised by adults who have the time and resources to care for them and support them through ALL emotions, not just happiness.
Everyone deserves to be able to express negative emotions and not be forced to appear happy all the time.