But the boys soon told their father about the discovery. "He asked them to go and get them," Mr Rouillac said. "But he initially believed they were knife holders that belonged to the grandmother."
He contacted Mr Rouillac's company to double check and, after sending a few photographs, he was told the good news.
The objects were not knife holders, but two gold bars weighing 1kg (2.2lb) each.
Both bars are now listed on the auctioneer's website with an estimated value of 40,000 euros (£35,800; $43,800) a piece.
It turned out that the bars were purchased by the grandmother in 1967 and even come with a proof of purchase.
Moreover, the price of gold has increased due to the coronavirus pandemic. "We are going to wait for the price of gold to rise a little more," Mr Rouillac said. "They could get at least 100,000 euros."