Nursing mothers face an energetic trade-off between infant care and work. Under pooled energy budgets, this trade-off can be reduced by assistance in food acquisition and infant care tasks from non-maternal caregivers. Across cultures, children also often provide infant care. Yet the question of who helps nursing mothers during foraging has been understudied, especially the role of children. Using focal follow data from 140 subsistence expeditions by BaYaka women in the Republic of Congo, we investigated how potential support from caregivers increased mothers’ foraging productivity. We found that the number of girls in early childhood (ages 4–7) in subsistence groups increased food returns of nursing women with infants (kcal collected per minute). This effect was stronger than that of other adult women, and older girls in middle childhood (ages 8–13) and adolescence (ages 14–19). Child helpers were not necessarily genetically related to nursing women. Our results suggest that it is young girls who provide infant care while nursing mothers are acquiring food – by holding, monitoring, and playing with infants– and, thus, that they also contribute to the energy pool of the community during women’s subsistence activities. Our study highlights the critical role of children as caregivers from early childhood.

During a total of 230 observation days, we recorded the time when focal women began and finished foraging-related behaviors such as collecting nuts, digging wild yams, fishing, or hunting. From these data sets, the collection duration of each food item was calculated. We recorded the presence or absence of the focal women's nursing infants for each expedition. During focal follows, we continuously recorded expedition group composition and identified each individual in the group. When focal women returned to camp at the end of expeditions, we measured the wet weight of the edible part of the collected items in the women’s basket with a scale before the food was shared or cooked. We were able to weigh collected food items from 140 expeditions by nursing mothers before the food was distributed or processed. We were unable to weigh food items that were cooked and consumed on-site in the forest during expeditions, such as a part of a fish, caterpillars, or animals that were caught. From 140 expeditions, we were able to weigh 223 food items, categorized into animals (one species), fish (multiple species), nuts (five species), wild yams (five species), caterpillars (four species), mushrooms (five species), leaves (three species), and crops (seven species), indicating that BaYaka women collected more than one food item per expedition on average (ranging from one to four food items). Species of collected food items were identified with the help of botanists from the Herbarium at the Institute de Recherche en Sciences Exactes et Naturelles (IRSEN) in Brazzaville in the Republic of the Congo. After identifying food item species, we calculated the energetic calories of each food item collected in a day by multiplying the total wet weight of the edible part of a food item in a focal woman’s basket by the reported value of energetic calories per gram. We calculated food returns per collection duration by dividing the total energetic calories of a food item collected on an expedition by the total collection duration for that food item across the expedition in minutes (kcal/min). Collection duration was defined as working time in minutes from searching to food acquisition, which varied depending on food types: the total duration of 1) searching and picking caterpillars, mushrooms, and leaves, 2) building dams, scooping water, searching, and catching fish, 3) chasing, making holes on tree logs, and killing porcupines, 4) digging wild yams, 5) picking and cracking nuts, and 6) digging and collecting crops, such as cassava, taro, and maize. These six food types were included in the statistical models as random variables to account for possibly different effects of food items.

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