Some of my favorite shots of my kids are the ones where they are "less-than-happy." Perhaps this is because it captures a real moment; the moments inbetween pasted on smiles and forced poses. They capture this life we are making our way through: tears and all.
The only advice I would give when shooting life's more difficult moments is: be discrete. The last thing someone wants in the midst of their trouble is to have an over-zealous camera mom in their face.
Capture daddy's way of soothing a newborn baby, or calming down a frantic toddler. Capture the interactions of siblings or the pensive moments following discipline.
Don't avoid the camera when life gets hard. If life is a bed of roses, don't forget the thorns.
Related Tags: Photo Tip, memory, capturing kids, child photography, camera mom