The exclusion of boys being raised by single mothers, which happens a lot. Many mosques now have a policy of not allowing boys into the women’s section from as young as age seven, irrespective of whether or not they’ve reached puberty.
Now in the time of the prophet (SAW – peace be upon him), that wouldn’t be an issue because the way mosques were set up, they allowed children to be in the back rows of the men and the mothers could then join the front row from