The little boy, 2, was playing with his dad at the Millennium Park in Illinois when he suffered cuts from the blades which had been hidden on slides, monkey bars and even on the ground.
His father was horrified, telling US channel KWQC: "It's something I can look out for now, if I'm ever here.
"We just kind of think about them swinging on the swing set or, you know, climbing the monkey bars. Don't really think about razor blades."
The shocked father quickly contacted police, who disturbingly discovered at least a dozen blades littered across the playground.
Lieutenant Brian Foltz confessed that he had never seen anything quite as horrifying, saying: "I've seen a lot of things, but not razor blades glued to equipment at a park.
"It's just a bad situation, bad instance where somebody or maybe a group of kids... figured this would be a fun prank to do."