Did those complaining about the title read the "Allegedly" part? It doesn't say "5-year-old Stabs Sister Over Nintendo DS"..
Allegedly: An allegation (also called adduction) is a statement of a fact by a party in a pleading, which the party claims it will prove. Allegations remain assertions without proof, until they are proved.
The mother alleged the kid did it, when it could very well have been herself that did it. Media is all about sensationalism, however, which is partially the case here. Perhaps a better title would have been "Mother Claims 5 year old Stabs Sister Over DS".. but the title for this article itself is not false either and I wouldn't be surprised if you found it worded the same way on other news web sites.