Final answer:
Infants can typically turn over from their abdomen to their back by the end of the fourth month. This is among various developmental milestones achieved during infancy, which also include sitting up and beginning to crawl by around six months.
Step-by-step explanation:
Infants generally achieve the ability to turn over from their abdomen to their back by the end of the fourth month after birth. At this stage in their development, besides rolling over, infants can also lift their head 90 degrees while lying prone, sit up with support, and maintain a steady head for short periods. This milestone is one of many that infants reach as they develop motor skills, sensory awareness, and cognitive abilities in their first year. It's interesting to note that by around six months, infants can not only roll over but also begin sitting without support and even start to crawl.