An app aimed at children that featured a voiceover making threats to cut them with a knife, has been banned by Google.
Blaze and the Monster Machines was removed from the Google Play Store following complaints from parents.
There is mounting pressure on firms to make their platforms safer for children.
One firm that offers real-time blocking software said Google "failed egregiously in its duty of care".
The unofficial app was based on a Nickelodeon show, also called Blaze and the Monster Machines.
The voiceover starts off in a friendly manner: "Hi kids, I'm your new friend! You see, I want to play with you kiddo. Maybe we could perform some fun games together."
It then takes a sinister turn: "You look afraid, is it this knife in my hands? Making you a little nervous? This knife is going to improve your look when it's sticking right out of you."
Following horrified reactions from parents, Google pulled the app, saying: "We have a set of policies designed to provide a great experience for users and developers and we act quickly to remove apps from Google Play that violate those policies."
Richard Pursey is chief executive of SafeToNet, a UK firm which offers to protect children from issues such as cyber-bullying, grooming and trolling with software that blocks such content in real-time.
He said: "While we applaud Google's response of taking the app down, it is simply too late. By the time content has been flagged to Google or any other app store, it will have been seen by millions of children.
"Unfortunately, this forms a fairly common trend. For example, recently, YouTube removed a children's cartoon called Paw Patrol that showed children sleepwalking to their deaths.
"This was viewed over three million times before it was removed. We have also seen clips of Peppa Pig drinking bleach and Elsa from Frozen using automatic weapons."
Children's charity the NSPCC urged parents to set up parental controls on their childrens' phones and have "regular conversations" with them about staying safe online.
The government is keen that social networks and other technology platforms take more responsibility for the content they carry.
In a speech at the World Economic Forum, Prime Minister Theresa May said that making tech firms into publishers was "very complicated" but asked whether there could be a new definition for them, which might make it possible to make them legally responsible for their content.