Yes, when those of us who are mothers whose sons or daughters died by suicide see other mothers happily with their children, it's a reminder that we can't be physically present with our children any more.
But I believe that we can still celebrate being their mothers, because our mother-child connection did not end the day they died. It just changed form. (It took a while for me to reach this point, though. The first few Mothers Days after Arlyn died were horrible.)