The most important thing when beginning a study like this is to pose a question properly. "Importance" is too broad and difficult to pin down the meaning. The question has to be one that can be answered by some acceptable process. So, for example, you might frame a question like, "Does the use of digital devices by children ages x to xx affect the time spent in outdoor play?" This limits what you have to look into and presents something to compare, "screen time" and "outdoor play time." Hope this helps you get started. If you ask the right question, then what to do next appears obvious. Good luck.