On a recent show Diggy stated that he was 10 years old, so that would make Russy 8 or 9. I thought they were a little older than that myself, but if this is correct then Russy's reading and his hyperactivity are normal for his age.
As for the show itself and all the the "down time", you can tell this is not like many reality shows,. I view it more as a "reality sitcom". This is not a "follow the family all day, every day show to see what we can catch". Something interesting comes up and the episode is built around it. The family and their reactions are shown only to add to whatever situation they are showcasing that week. Because of this we see them in certain aspects of their day and not doing everything that they do throughout a day.
During the season finale where the social worker came to address the adoption issue, it was so sad when Justine started crying and the look in Diggy's eyes. It's good that they don't just sweep the baby's death under the rug on this show but they also don't show them wallow in their sorrow. It's an excellent balance of perserverence and sorrow.