This study examined young children's information‐seeking behavior for illness or injury by (1) identifying primary informants and (2) determining whether children's evaluations of trusted informants change with development. Studies 1a, 1b, 1c, and 1d showed that 3‐ and 4‐year‐old children preferred to ask adults, including experts, as well as familiar and unfamiliar adults, for illnesses and injuries, but did not prefer to ask other children and stuffed animals. It was also shown that 3‐ and 4‐year‐olds' previous experiences of medical examination were not related with their preferences of informants and that they valued doctors' information about specialized knowledge more than mothers' resources. Studies 2a and 2b examined whether evaluations of trusted informants changed with age. Adults tended to differentiate between informants for contagious and allergic illnesses. However, this differentiation was not observed in 4‐, 7‐, and 10‐year‐old children. Adults preferred to seek help from doctors rather than mothers for contagious illnesses and injuries, whereas for allergies they preferred mothers to doctors. However, their reliance on mothers was limited. Preferences for mothers were not observed for nonallergic illnesses, such as headache, toothache, and cancer. Highlights Three‐ and four‐year‐old preschoolers preferred to ask adults, including experts as well as familiar and unfamiliar adults, for help with illnesses and injuries, rather than other children and stuffed animals. Three‐ and four‐year‐olds valued doctors' information about medication and causes of illness more than mothers' resources, though such preferences were not observed for daily advice, such as dietary and rest for sick individuals. With development, evaluations of trusted informants in the domain of illness changed. Adults tended to differentiate between informants for contagious and allergic illnesses; however, this differentiation was not observed for 4‐, 7‐, and 10‐year‐old children.