I hope this will be helpful to OP. I am the quintessential sleep in person in real life. I get up earlier at Disney than I do at home, because it is worth it to ME. It is not worth it to some people. I did once go on a Disney trip when one person who usually is a morning lark decided to sleep in. This was in June, so I think it is similar to the trip OP plans. Some things OP should be aware of:
1. When you get to a park in the crowded, hot summer at 10 or 11, there can easily be an oppressive crowd waiting to get into the park. That is OK if you are mentally prepared to deal with it. It is very disheartening if you are expecting the kind of entrance crowd you see at rope drop or in October.
2. Different people have different ideas about how many rides/shows/etc they want to do and how much reduction is dissatisfying. The lines for attractions and QS food can be quite long during much of the day.
3. At night SOME lines shorten because some people run out of steam and go back to the resort. Being able to take advantage of evening EMH, especially with hoppers can really help.
4. If you really want to see a lot, and you really want to sleep in, you may want to skip the break. Despite what some people say here, a person can wait through the lines and see some attractions during the heat of the afternoon. In fact, some attractions are more conducive to this than others.
5. Eating at odd times, especially those meals where you do not have ADRs can be an advantage--you are experiencing attractions when others are eating and eating when the lines for food are not quite as long.
6. Depending on your preferences, minimizing time spent for breakfast may be helpful when you are sleeping in.
7. Take into consideration when you plan to get to the parks as you plan your days. A good plan is probably MORE important if you want to sleep in AND see most or much of what there is to experience.
I hope the OP and her son have a magical vacation. My main recommendations (the ones I see as most important) if they want to sleep in are plan park days, do not break, stay late, and expect both heat and crowds.