I see Time Bandits. I really think that Larian may have used real people of short stature to model their halflings. It makes sense in many ways, but may not be the image that some people have of what a halfling should look like. The relatively big head might be due to animation restrictions, allowing the same algorithms to animate every potential PC's face. I am not a programmer so this is pure speculation.
I certainly prefer the current look to having them look like children. I think that was a major mistake for Pearl Abyss in BDO when they introduced the Shai. They jumped through hoops to say that the Shai were not meant to be child-like, but then portrayed them in-game as child-like (using child-like voices and having the NPCs dancing and playing like kids). The Korean anime-style art style didn't help, of course.