If a domestic servant does something we tend to count this as work, with all the connotations of that word and status, but if a wife or child does it, we don't.

It's a stretch to say that gender or age has anything to do with not counting it. Men's household work is not counted either after all. The reason for not counting it it's because data on it is hard to get and it wouldn't give you much useful economic information anyway: most economics is interested in change over time---the level of household production does vary a little and there are some interesting long-run trends (e.g. a decrease from the middle ages to now), but these changes are simply dwarfed by the changes in non-household production in both the far and near runs (there is just a lot more room for growth in the commercial and industrial sectors.). In fact the level of household production generally increases when things get bad (e.g. the number of people who occupy themselves with mending their family's torn pants goes up when people have relatively more time than money---i.e. when unemployment is up. ), but it's probably not all that useful tracking those change in too much detail, not just because it's hard to get detailed data for, but it wouldn't tell you anything you didn't already know from employment figures.

I think this discussion gets a little sidetracked by equivocating "counting" with "acknowledging as important". Just because it isn't widely reported in economic data doesn't mean anyone in the profession would say it's not an important aspect of life. The most politically conservative economists are likely the ones that would place a high value on it as it's part of "family values", ironic because this is generally a feminist critique of economics.