How can gvmt in your opinion promote large families?

Stop the funding of abortion and contraception would be a start.

The US government could send to each mother the daycare subsidy they send to the daycare.  This amounts to about $150 a week.  And offer NO subsidy to working mothers.

This would go A LONG way to encouraging married, traditional families.

Also the government could offer a housing allotment to families with more than 2 children.  

They could also make a midwifery subsidy, where child-birth is free or based on income.  The children could be born at home or in local birth centers.  This would encourage more women to get into midwifery and make child-birth a normal process again instead of a disease or illness that needs to be treated at a hospital.

The USA gov does assist large families who are low income. Every child is entitled to food stamps and some form of health insurance. OB and pediatric care is covered for the delivery. There is WIC providing some food for pregnant women and children under 5 I believe.

There are other programs too that are limited like rural housing loans.

These programs don't actually provide all that much help to large families unless they are very poor or very large.  And each state is different.  We used these programs once upon a time.  My husband made about $47K and we had 6 children.  We received $211 per month.  That equated to  just over 1 week of groceries.  Some states, like ours, now excludes you from SNAP benefits if you have a savings account or if you have 2 cars.  

The WIC program is nutritional deficient.  They are changing some items but most of the items we didn't even eat, like cereal, baby formula, and baby food.  Some states have changed their WIC program to include $25 a week of produce but not white potatoes or bananas or legumes of any kind.  

The health insurance can also be very restrictive.  I had to use Medicaid once when my husband lost his health insurance through work.  I was pregnant with my 4th child.  I had to drive over an hour to see the OB GYN and in a very unsafe neighborhood.  I had to deliver at a hospital also over an hour a way.  Also, these programs make you take a class on Birth Control.  And while they don't force you to use birth control, there is a lot of pressure to do so.  Also to keep your benefits for your baby, you must vaccinate either at the state clinic or a Dr. approved by them.

The housing benefits are very inadequate and actually encourage single parents with no income.  Once you go to work or if someone has a half-decent job, the benefits are lost.  I have a friend, single mom, with 2 kids who got a job making $11 an hour.  She was getting $850 housing subsidy.  Now she gets nothing.  At $7 an hour, she could get $475.

The programs in this state and our nation actually encourage single parents with children and discourage traditional families with many children.