A new research, carried out by Christopher Bartneck from the University of Canterbury, New Zealand, claims that Lego characters, which are now getting "angrier" over the years, could affect development in children.
Close study revealed that previously, Lego human characters had happy expressions; however, since 1975, there has been an increase in the production of angry faced Lego characters.
This increase in the production of angry Lego toys could have a negative impact on children, the researchers say.
The six most common and prominent facial expressions noted in Lego characters today include anger, concern, fear, confidence, disdain and happiness, they add.
"Analysis shows that toy design has become a more complex design space in which the imaginary world of play does not only consist of a simple division of good versus evil, but a world in which heroes are scared and villains can have superior smile."
It was 1990 when Lego began to experiment with the facial expressions of its human toys, and they stuck to one smiley face for the first 11 years. It was after that they started introducing angrier characters.
"We cannot help but wonder how the move from only positive faces to an increasing number of negative faces impacts how children play," Bartneck said.
"Designers of agent faces should take great care to design the expressions and to test their effect since toys play an important role in the development of children."
Lego, one of the biggest toy manufacturers in the world has produced over 36 millions bricks, distributed to more than a hundred countries in the year 2010 alone, which equals to 75 bricks for every person on the earth.
Since toys play a huge role in children's development, these angry Lego toys could be an issue of concern, the study explains.
"Lego themes have been increasingly based on conflicts [such as Pirates or Harry Potter]. Often a good force is struggling with a bad one," Bartneck added.
"The facial expressions are not directly matched to good and evil. Even the good characters suffer in their struggle and the villains can have a smug expression. In any case, the variety of faces has increased considerably."
Bartneck is expected to present his paper at the first International Conference on Human-Agent Interaction in Sapporo.