Paul and Marie had four children, two sons named Robert and Marcel, and two daughters named Georgette and Fernande. The early years of Cantillon produced unblended lambic, mars, faro, gueuze, and kriek, and framboise. After the First World War, Paul was ready to expand the business and bring his two sons into the fold. Finally, in 1937 Paul, Robert, and Marcel purchased the Brasserie Nationale du Néblon located in Ouffet which had closed the previous year in 1936. They moved the brewing equipment to its current location and the first batch of Cantillon’s own beer was brewed in 1938 shortly before the brothers were called to mobilize for World War II.<ref name=GeuzeKriek />
During the Second World War, with supplies in demand for the soldiers, it was more difficult to continue to brew beers. The period during the war saw the brewery at a near standstill. The immediate post-war years did not see the same demand and production of beers as the 1930’s had. To make matters worse, a massive heat wave in Belgium destroyed many brewery’s stocks including Cantillon’s. Sometime around 1950 the brewery began to recover and reached an all-time high production in 1955. Paul Cantillon passed away in 1952, while his wife Marie lived until 1958. Starting in 1960 the demand for traditional gueuze and lambic began to decline once again and Marcel Robert sold his share to Robert Marcel and left the business. RobertMarcel, too, was on his way out of the brewing business when his only daughter, Claude, married Jean-Pierre Van Roy. By 1969-1972, Van Roy had taken the reins of the brewery.
To keep the brewery afloat, Van Roy sweetened his gueuze with artificial sweeteners to keep up with current tastes. Sadly, this did not help the brewery and it continued to operate at a loss. By 1975 Jean-Pierre began to abandon the artificial sweeteners and stopped the practice altogether by 1978. In 1978 he also decided to create a working exhibit dedicated to the art of lambic brewing. Opening Cantillon to the public allowed them to bring some extra revenue to help balance the books. It also helped to spread the word to both locals and to tourists. <ref name=GeuzeKriek></ref>