Cognitive development refers to your child's ability to learn, think, and problem solve. While every child develops at a different rate, typically by the age 6 and 7 your child's ability to learn shifts through learning through observation and experience to learning through language and logic. They're now involved in abstract thinking.
They have reasoning skills. This is the time where you want to get them really engaged in more complex problem solving. Think of games like Clue, the who done it. This is a great way for your child's mind to continue to make those connections and to learn even more. At this point also your child will be able to make the right decisions.
They have a much longer attention span. They know the days, the months, the seasons. And they're really able to use much more complex problem solving skills. So this is really again a great time to encourage those skills to emerge and grow by playing games, again such as Clue, Battleship. Anything involving this more higher level thinking is really a great way to get them to continue to learn and grow.