Hi Emphaticmaybe,
Marxist feminists have historically given a lot of thought to your concerns and it's one of the major strands of marxist thinking. You are right, if women's work is devalued but women want parity with men in the workplace there is the question of who picks up the mop and how that should be remunerated. There is obviously always going to be the problem that all work that is undervalued is underpaid, under the capitalist means of production it is unavoidable. The worker in the case of the cleaner/child carer must create surplus value for their employer, ie you must have a percentage of your wages left to you after all costs. Just imagine what the cleaner/carer has left after all expenses?
It is not easy to solve because all capitalist means of production and exchange must create a surplus profit for employer. A commodity must be sold for it's value in terms of all inputs including labour time, it effectively means that as you exchange labour time for a small proportion of the value created you have less money to buy less commodities.
Most Marxists/socialists would argue for three things, workers ownership of the means of production and a share of all profits, minimum wages and state sponsored childcare. The primary reason for state sponsored childcare is that childcare is then properly funded, is available to ALL women regardless of class/marital status and finally that women who undertake care should be rewarded with a share of the surplus, ie government ownership of some means of production should with taxation create a surplus to look after the poor, unwaged, full time carers etc,,,,from each according to his ability, to each according to his needs.