This problem is an example of when we need to take a weighted average. We simply can't just find the average of 5 and 8, because there are different children of each each.
To start, lets multiply the total number of children by their individual ages.
6 x 5 = 30 years 14 x 8 = 112 years
There are 142 years among the 20 years, so divide 142 by 20. This gives us an average age of 7.1 years.
