I think if Conservatives could get over even a little bit of their ideological stance on small state / public funding, they could make a really good case for supporting women to be SAHM.
If stable, happy families would overall lead to better outcomes for children (and by extension the adults they grow into) then supporting this would provide significant future savings in terms of welfare and health spending.
It seems to me that there are many women who would like to stay at home and look after their children in the early years, but feel pressured to work either due to economic necessity or social pressure as it's not something a 'modern woman' should be engaging in.
I've also come across women who would like to have more than two children, but again don't feel able to do this due to economic constraints and social stigma.
It seems like a good opportunity for Conservatives to advocate for some sort of policy whereby SAHM receive a living wage plus pension/NI contributions from the government for X number of years for each child. Crucially, the payments go directly to the individual women and not as part of a consolidated household payment. Similar sort of payments would apply if it was the husband that stayed at home full-time, or in the case of same-sex couples whichever partner took on that role.
And maybe tax breaks or eligibility schemes for affordable housing for those families where one parent is a full-time carer in comparison to where both partners are working.
The role of tax, apart from reducing the overall supply of money to control inflation, is a way for governments (whether left or right) to nudge citizens into desired behaviour - increasing tax to discourage certain behaviours or decreasing tax to encourage certain behaviours.
But it does require acknowledging that governments do have an important role to play in shaping the societies we live in, and of course as citizens we decide on the type of government we want. And it does mean accepting that there are limits to capitalism / free markets and we should not let it dictate how we run important aspects of our society.