Dear Luke,
This is a tricky table to interpret - the labels and description aren’t as detailed as they probably should be!
The key thing to know relates to the “With own children under 18 years: Under 6 years and 6 to 17 years” category. Based on what you have calculated, you have this category as being women with children (e.g., the sum of E4L007 through E4L009 is the count of all women with children).
Unfortunately, that category counts the number of women with a child under 6 years of age AND a child 6 to 17 years of age. These women have at least two children, and they have a child in each age category.
You should sum all the categories E4L001:E4L012 to yield the universe (all females age 16 or older). The count of women with children will be the sum of E4L001:E4L009 - that is your numerator.
Dave Van Riper