Aren't there cameras that monitor those rooms?
Not in the pediatric ICU's, either med/surg or cardio, I've been in. Heck, even in ones with private rooms, there are no cameras. There are big, sliding glass doors with curtains you can pull across for privacy. Heck, I think the only place I've seen cameras in the children's hospital I'm most familiar with is points of entrance/exit for the floor and the hospital itself (so at the public and staff entrance, the elevators and the fire exits).
From some Googling, it looks like the ICU at CHO is an older, ward-style layout with curtains to separate beds and some semi-private rooms rather than a full private room layout. But if the patient is relatively stable, then families are often allowed to pull the curtains closed for extra privacy. After all, if things start going south, a bevy of monitors will start wailing immediately to alert the nursing staff.
The ratio of nurses to patients at the PICU and CVICU I'm most familiar with is 1 nurse to 2 patients. There may be 1 nurse to 1 patient in a case where the patient is extremely unstable. But even in a 1:1 situation, there are times a nurse might have stepped out of the room for a variety of reasons, especially if family is present. Of course, if the patient is actively unstable, this won't happen. But many ICU patients are stable (or their version of it) for long stretches at a time.
And FWIW, I spend most of my time on a non-ICU floor but one that always has a handful of NPOs (nothing by mouth), and you'd be amazed at how really well-meaning parents will ignore that direction when their child is hungry. I don't know if that is what happened in this case, but it's certainly not something that would surprise me given how often I've seen it happen.