I agree moms who would not be able to work while raising babies/toddlers, or simply prefer not to, shouldn't count as members of the labor force.

However. It is very difficult to determine what makes a mom employed vs not employed. Is that by choice/preference? or lack of opportunity. Or lack of qualification, or a combination. Coming up with statistics that distinguish the two is nearly impossible.

The official rate does not only exclude moms who happen to be jobless. It excludes anyone hasn't been actively looking any more.