See:
https://phys.org/news/2019-05-grandm...or-family.html

"Since the ultimate goal of any living organism is to spread their genes, the evolution of menopause in women has been quite puzzling for scientists."

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But what if menopause actually favoured collaboration between generations? The grandmother effecthypothesis suggests that menopausal women might still be able to increase their genetic footprint, despite not reproducing anymore. They do this by helping their children to raise larger families."

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Historical human population data are valuable to study the grandmother hypothesis because detailed life-history events are recorded over multiple generations and family relationships are well documented. The positive impact of the presence of a living grandmother on her daughter's family size has recently been shown in a study of pre-industrial populations of Québec, shedding light on mechanisms that could explain the evolution of menopause."

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Having a living maternal grandmother increased the number of offspring born by their daughters by about 20 per cent. It also had a positive impact on the number of grandchildren that survived to age 15. When a grandmother was alive, the daughter's age at first reproduction also tended to be lower, expanding her reproductive opportunities.Similar results were also reported in other pre-industrial populations. Finnish families raised when the grandmothers were alive were larger than when the grandmothers were dead. In the German Krummhörn community, the presence of maternal grandmothers decreased grandchildren mortality between six to 12 months.
Having a grandmother around to lend a helping hand seems to have a significant impact on child survival rates and on family size. At least this is what the grandmother hypothesis is all about. But church records, however meticulous they may be, provide no indication regarding the involvement of the maternal grandmother in the rearing of her grandchildren. After all, a grandmother may be alive but not helping her daughters at all."

"Another study conducted on a Finnish population also found some limits to the grandmother effect. They revealed that the presence of maternal grandmothers increased the survival of grandchildren, but that the effect decreased, and sometime had a negative effect on family size, when the grandparents were getting older."


I'm not sure about the menopause connection, but having a mother nearby to help with the children, just as a practical matter, would definitely lead to larger families.