I realize your post was a while ago. I just joined, so I am seeing it for the first time.
I have two sons, 6 and 7. They both act this way at mass. My 7 year old is better than my 6 year old. My 6 year old actually puts his head back and pretends to sleep. I am constantly telling him to pay attention and so forth. One thing I have found that helps is reminding him right before we walk into church about how to act. I feel that little reminders that are not lecturing or punishing in tone help. This does not make him behave perfectly, but it helps. Also, our parish has children’s coloring/work papers at the door. They pertain to what we are learning at mass that day. So, the children can participate at their own level. I always grab one and it keeps his focus on what we are there for for a short time. I realize they shouldn’t be coloring, but paying attention. So, I make sure they are only using the paper when we are sitting. I have them stop when we are standing or kneeling.
I am still trying to find ways to get my children to behave better. If you have learned anything new since your post, please share.