Big Families in Ideal conditions
The Bible says that fields should lay fallow for 2 years in order for the soil to regain its nutrients. Is a womb no less precious than a field? It takes about 2 years for the womb, the bones and the body to optimally regain the optimal nutrients and bone density to order to carry out an optimally healthy pregnancy and birth.
God also prepares the body for this for when the body works correctly through on-demand breastfeeding for 2+ years, for the average length of time for the menses to be halted is anywhere from 12-34 months. The World Health organization, as well as many other health entities states that optimally a child should receive breastmilk for at least 2 years (or for as long as the mother and child wishes - the average age of weaning world-wide is from 4-5 years of age). This would naturally mean that children would be spaced 3 to 4 years apart. I believe that this is God's biological plan for the best possible health of mother and baby.
If you are having just 2 children, and you decide to have them around 18 months apart, well, it will be harder on your body, but it probably won't have any lasting detrimental effects. The problems start when women decide to have many children close together. Bodies and health break down and problems start to ensue either with the mother or the baby.
God also created the natural laws of fertility. The average woman becomes pregnant between day 12 and day 16 of her menstrual cycle. If you have an irregular cycle, then it is more difficult to chart. Charting though helps all women know and learn about their own bodies - not only to know when you are fertile, but also to know when something is wrong and if you might need to see a doctor. There are many books and websites on how to chart your own cycle. God also has created many plants and herbs that can help regulate your cycle, as well as heal the reproductive system. I have known many women who have healed endiometriosis, fibrous tumors, irregular 40 day cycles, etc. all through the healing properties of God-made plants.
Another issue to consider is that the first 3-4 years of a child's life are very important and needs a mother's full attention, care and training. This also allows a mommy to be a mommy, and not a delegator. I have noticed that as long as there are only 5 children/teens in the house at one time, a mommy can stay a mommy. More than 5 and often mommy becomes a delegator/facilitator, and the older siblings must spend a lot of their spare time helping to raise their mother's children. Also, if you do choose to place your children in school, you would never have more than two little ones not in school. This will help faciliate care and training.
If a woman begins having babies at 22 and continues through age 46: At age 46:
3 years apart: Children are ages 24, 21, 18, 15, 12, 9, 6, 3, Infant - Total - 8 Children 4 years apart: Children are ages 24, 20, 16, 12, 8, 4, Infant - Total - 6 children 5 years apart: Children are ages 24, 19, 14, 9, 4 - Total - 5 children
So according to God's plan, even if you started at age 18, you will most likely only have 10 pregnancies at most, and more likely to have only 5 to 8 pregnancies if you begin in your twenties. Another blessing to this is that there will always be a little one (age 5 or younger) in your household. For by the time your youngest is 5, you will be 51ish and your oldest three will be in their twenties and surely one of them would probably have provided you with a grandchild by then!
If you start your family in your thirties, it is still possible to have 4 or 5 pregnancies three years apart before becoming menopausal. And menopause is often delayed through both pregnancy and breastfeeding. And maybe God will bless you with twins! Or in the case of one supposedly infertile couple in their 40s that I know - they adopted triplet babies - and then became pregnant with twins! 5 babies in the family within the year - now that's starting a large family with a bang! God can provide a family in unexpected ways.
Sometimes your genetics or your environment or your diet or your breastfeeding methods warps the body and does not halt the menses for 12-34 months. It is still ideal to follow the natural laws God put in place and withhold from intercourse (while you are ovulating) for the first 24-36 months after birth. For more information, there are many articles and websites on Lactational amenorrhea and how to ideally achieve it. There is also a lot of information available about charting and ovulation through books and websites - remember, this is the method that God has put into place so that you can keep your womb fallow for at least 2 years in order to replenish your body with important nutrients.
I also know many women who tandem breastfeed (breastfeeding an older child and an infant), and so choose to breastfeed for over 30 years of their life. There are many God-made herbs and supplements that help enrich the milk to be best for your child/children, as well as helping the mother to maintain her health, energy, nutrients and bone density.
There are some women who are just truly made to be mothers and who truly desire a large family. If you stick with God's plan, and rest the womb for at least 2 years before becoming pregnant again, and if you educate yourself on the healing and energizing properties of God-given plants and herbs, then you and your babies will ideally lead a healthy and abundant life!
* Caveat: This is an optimal plan for an ideal way to plan a large family - this is in no way a judgement or bias against women who choose differently.