Answer: Parents and children ( till the age of 5) of Norway
Step-by-step explanation:
Here, A large study of over 2000 parents and children in Norway found that toddlers who regularly slept less than 10 hours per night or woke frequently (three or more times) at night tended to experience more emotional and behavioral problems when they reached age five.
Since the study involved a large random sample of mothers and children and was conducted over several years.
So, the population of interest in this survey is "Parents and children ( till the age of 5) of Norway".