I think you're missing the point of the "childcare is not part of the workforce" argument. It's not that it isn't work, and it's not that it isn't important. It's that, in many cases, the economic comparative advantage for the (often) female caretaker of those children is not being fully utilized.
That is to say, caring for a child is a service that costs X. But it is being performed by a person who's skills are valued at Y, where Y > X. That represents an economic loss that doesn't have to happen, if instead you substitute someone who's most highly valued skill is worth X for that caretaker.
Now, that ignores the benefit of having a child's own parents care for them, which may or may not change how you evaluate the question depending on your perspective on these things.
That is to say, caring for a child is a service that costs X. But it is being performed by a person who's skills are valued at Y, where Y > X. That represents an economic loss that doesn't have to happen, if instead you substitute someone who's most highly valued skill is worth X for that caretaker.
Now, that ignores the benefit of having a child's own parents care for them, which may or may not change how you evaluate the question depending on your perspective on these things.