Kim De Gelder, 24, told of a difficult relationship with his parents, a teacher who beat him and a psychologist who laughed at him, FlandersNews.be reported Tuesday.
"If society is cruel to me, then I can be cruel to society," De Gelder said.
In addition to the two toddlers, De Gelder is accused of killing a 54-year-old nurse and injuring dozens of other toddlers during a stabbing rampage.
De Gelder was wearing black and white face makeup and bright red hair when he burst into the Fabeltjesland nursery in January 2009 and began stabbing children, police said.
He laughed in court Tuesday when he was shown gruesome photos of a 72-year-old woman he is charged with killing several weeks before the daycare rampage, Knack.be reported.
De Gelder disguised himself as an employee of the water company to gain access to her home.
His trial centers on whether he was sane at the time he committed the murders.