While this is a terrible thing and the parents should be charged.... THIS IS NOT MURDER unless it was intentional.
How many times in past times did children get a hold of chemicals and die? Were those parents all charged with murder?
Yes this is neglect, but not murder.
I suspect the murder charges stem from failure to seek medical help immediately upon discovery and continuing to delay until the child was in extremis. Those are all acts of deliberation that meet the criteria for felony murder.