i never set any villager's preferred skill to parenting. even the nursing moms preferred skill is either set to farming or researching. although i have a lot of esteemed elders with master parenting skills, but their preferred skill is set to either research or farming as well, never parenting. but maybe that's the culprit behind it, once they've learned it, they just can't stop themelves from doing it again. i just wish my females are not always fertile.