Young mammals rely on rapid growth of the stomach and intestines to transition from milk to solid food, but the hormones that guide this process are still being discovered. One such hormone is apelin, a protein naturally present in the digestive tract and in milk. We asked whether giving apelin directly into the stomach of newborn rats would change how their stomach and small intestine develop. Ten-day-old rat pups received apelin or placebo for two weeks, after which we examined the tissues and measured the thickness of the gut wall, the size of surface cells that absorb nutrients, the mucus-producing cells that protect the lining, and the structure of nerve networks inside the gut that control movement. We also measured two appetite-related hormones made in the gut, ghrelin, and leptin. Apelin made the stomach lining thicker and changed some digestive cells, and it reshaped the small intestine depending on the region, with stronger effects in the upper part. The gut nerve networks and local ghrelin and leptin signals also changed. These findings show that apelin can influence early digestive development and may help explain how feeding hormones program gut function in infancy, which could be useful for improving neonatal nutrition.