To sort or not to sort
All large sets released in the last few years come in numbered bags. The bags are sorted by logical sections as they appear in the instruction manuals. So for example there will be several bags numbered as #1, several bags numbered as #2, etc. 

The intention is that you open all the bags numbered as #1, build that section, then open the bags numbers as #2, etc. This makes building a lot easier, faster, error-free, and a lot less messy. 

In very large sets each section usually takes about an hour to build, and the whole set can take 2-5 hours to put together. While some LEGO fans do building marathons and put together sets in one sitting, for most people stretching out the building experience to several days is less stressful and more practical. 

Also, note that numbered bags usually allow several people to work simultaneously as, the numbered bags tend to represent chunks of the set that later get assembled. This makes the building process faster. So for example your son would be building the first floor of a structure, while you can work on the second floor.

Another way people work together on large sets is for one person to be the sorter, and the other the assembler. In your case, this may mean that you find the parts for each step of the process, and maybe even build some of the small assemblies, then you hand them to your son who will attach them to the set.

All in all I would say that numbered bags are your friends. The larger the set, the more you will appreciate their practicality. There are still old-school LEGO fans from the pre-sorted bags period, who build differently. They may dump all the pieces from all bags into one pile, or open all the bags and pre-sort pieces by type or color. But for most people, building the way LEGO suggest is the best way to tackle large sets.