I was a reading tutor and worked with about 20 different kids in grades 1-3. Many of the third graders had problems with tracking when they started the school year, but this improved over time. I would say that it's developmentally apprporiate for a 7 year old to have issues with this. My second grade 8 year old with DCD does not have these tracking issues but I think he had a few issues with missing words or entire lines a year and a half ago. When he read out loud he would blow right through periods and other punctuation as well like they didn't even exist.
