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, kriek, and framboise. After the First World War, Paul was ready to expand the business and bring his two sons into the fold. 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 1930s had. To make matters worse, a massive heat wave in Belgium destroyed many breweries’ 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 Robert sold his share to Marcel and left the business. Marcel, too, was on his way out of the brewing business when his only daughter, Claude, married Jean-Pierre Van Roy. By In August 1969-1972, Van Roy had taken agreed to take the reins of the brewery.From 1969 to April 1970 Jean-Pierre apprenticed with his father-in-law Marcel Cantillon, learning the trade. <ref name=Trends>Jean-Pierre Van Roy interview, Trends Family Business, November 2017. [http://acties.trends.knack.be/acties/trends/familybusiness/archief/2017-11/portret-1.jsp "Hoeders Van De Traditie."]</ref>
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 the brewery 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>