Question: My son wants to know how the French fries he has at fast food chains are made?
Answer: You asked a very good question. The simplest way to answer this is to show him the basic steps that potatoes go through to become a fast food fry. This link from Ore-Ida illustrates 15 stops along the way to converting a raw Idaho potato into a frozen French fry that can be prepared at home in the oven or at a restaurant in a French fryer.
Long ago when the idea of fast food was first being expanded thru franchising, most places that served French fries in the United States used a russet potato, which they cut by hand (later by wall mounted or table mounted fry cutters such as this one.) By the way, the very best potato cutter in my opinion is also the one that costs the most, about $300 called the Keen Kutter. Many independent and emerging chains use the Russet Burbank variety from Idaho as it has consistently high solids or starch content and fries up crisp and golden.
To make a perfect fry takes some special efforts, here are links for foodservice operators as to how to do this from scratch, or check out this video on making signature fresh French fries, or follow these tips for frozen.