
Welcome to Stamp Community Forum, Warren!
Some people use some philatelic inventory software, but I find that limiting. But if you are a collector of a specific country, it might be a little more practical.
I use 2 ways -- old-fashioned and computerized.
The old-fashioned way, I just mark with a red pencil the stamps I have on the catalog pages.
The computerized way, I use an Excel spreadsheet to list the Scott catalog and catalog value.
As you may have guessed, I've got maybe 1% of my stamps "inventoried". It's more fun to sort/ID/enjoy stamps than it is to inventory.
Hope your son will really get into collecting! We need the younger generation to keep coming in!

Kim