Mental time travel describes the human trait of being able to imagine ourselves in time. We can remember that yesterday we ate cornflakes for breakfast, and that 2 years ago we were caught in a rainstorm and were soaked to the bone. We can also propel ourselves forward in time to imagine countless future possibilities and scenarios.
This skill is essential for so much of daily life, such as planning and preparing for upcoming situations. What use is practicing the piano if you can't envision a future where you will one day be able to play better than you can now? Why take an umbrella with you if you aren't able to imagine that you might get caught in the rain?
The capacity for mental time travel comes online piece by piece during early childhood and is usually in place by the time children start school. What is likely though, is that children understand much more, much earlier, than they're able to express. Research often relies on children's capacity to explain their thinking, a highly complex task (even for many adults!).
A carefully controlled study (by Australian researchers) had 4 year olds play in a room with a toy that had a missing piece. Some time later, they were given the opportunity to take an object with them back to the first room. The 4 year olds, but not younger children, often chose an object that closely resembled the missing toy piece, meaning they could remember and solve a specific problem they had seen previously well enough to prepare for its future solution.
These results suggest that before they reach school, around age 4, children have developed some of the fundamental capacities for foresight, future planning and problem solving. All capacities that will continue to develop throughout childhood and adolescence and be necessary for a successful future. Whatever that future holds!
References: Suddendorf & Redshaw (2013); Suddendorf, Nielsen & von Gehler (2011).