Colorectal cancer diagnosed in adulthood can originate from DNA damage caused by colibactin-producing bacteria during early childhood.

Study: Colibactin genes are highly prevalent in the developing infant gut microbiome

This study found that many babies have a type of gut bacteria that can damage DNA, and this happens during early childhood — the same time the claim says damage might start that leads to colon cancer decades later. So yes, it supports the idea.

Study: Geographic and age variations in mutational processes in colorectal cancer

This study found that a type of harmful bacteria called colibactin-producing E. coli leaves a unique DNA damage signature in colon cells, and this damage shows up more often in people who get colon cancer when they're young—suggesting the bacteria may have hurt their DNA when they were kids.

Study: Early-Life Mutagenesis and the Rise of Early-Onset Colorectal Cancer

This study suggests that harmful bacteria in the gut during childhood can accidentally damage DNA in the colon, and that damage can lie hidden for years until it turns into cancer in adulthood.