Finding the reason why it is ok for pregnant and breastfeeding women came from an understanding of why infants should not eat honey. Let me lead you through what I found. It was hard to find a single scholarly source of the risks to infants under 12 months, and it took reading a few to have a complete understanding. This online resource from Kid's Health had the best overview based on all the reading I did.
All honey carries the risk of being contaminated with spores from a bacteria that causes the illness infant botulism. The digestive tract of a baby under one year old is immature in several ways. Infants do not have all the normal flora (healthy bacteria) of an older child or adult to compete with the bacteria spores that cause botulism. The spores are then able to set up shop in the infant’s digestive tract. Additionally, the pH and decreased mobility of the infant’s bowel may also place a role in their susceptibility.
Adult botulism from food ingestion is extremely rare. The digestive tract of adults and child older than 12 months is able to move the spores out before they can cause harm. Thus honey is considered safe for pregnant and breastfeeding women.
While the number of cases of infant botulism remains low, less than 100 per year, avoiding honey is a smart tip to protecting your little one. Infants do not need honey and avoiding is generally easy. However, it is good to note that cooking or baking the honey will most likely not destroy the spores (need to boil for 20-30 minutes).
In addition, after all of my reading, I would probably avoid feeding a baby under 12 months home canned vegetables for the first year of life. This is not something we routinely eat, so avoiding would be easy for me. If you do consume home canned vegetables, make sure the cook is following proper canning techniques and it may be best to boil before consuming. This resource has more details
Pregnant or breastfeeding? Eat your honey! Under the age of one? Steer clear! If you do find out your little one consumed honey, don’t panic. While the risk is low, I would keep my eye out for any concerning symptoms mentioned in the first link, as it could take up to one month for symptoms to present.