You know what would encourage women to have more children:
A working CMS system which means men can't essentially stop paying for their children
Cheaper and more secure housing
Better childcare provision
Better paternity leave
Flexible jobs that encourage parents of both sexes to have the flexibility to do school drop offs and pick ups etc
Less zero hours jobs with all the instability they bring
No gender pay gap
Do you know what wont encourage women to have children:
Taxing them from 18 or whenever so they have even less chance of getting secure housing, even less chance of saving to adequately support themselves during their maternity leave
Making it easier for men to be more financially secure by having children (by avoiding tax) whilst still not making it harder for them to escape paying for those children
Also chillingly
Given how low the rape conviction rate is
And how some rapists are successfully managing to get access to children granted that are a result of the rape
Any tax that incentivises having children could easily lead to an increase in rape against women of child bearing age