I sometimes hate to be such a cynic, but these stories always make me wonder if some parent or guardian is an attention-seeker. There's a whole mental syndrome -- Münchausen Syndrome by Proxy -- where a guardian or caregiver seeks attention through the ill health or accident of their dependent.
That's just me being cynical though. It's really hard to imagine any parent allowing this to happen to their 2 year old, so it's probably a case of legitimate scumbags. Just who could put razor blades on playground equipment? We're plumbing the depths of depravity.