It's both though, and really the only way we're going to get a Halfling figure that isn't easily mistaken for a child is to hold pretty strictly to the 1:2 ratio, or go even smaller.
The average height of a human child is already 36 inches by age 3. Many are at that height before they can even navigate stairs properly. So making Halflings shorter than that with regular adult-Human proportions would go long way towards making it clear that they're Halflings and not Human youths. This wasn't a problem when Halflings were all goofy big foots like the Hobbit cartoons, but now that D&D has gone for something rather less cartoonish in the overall look for the Halfling, we need more to establish the new visual conventions. Right now all the Halflings look like Dwarves to me, not Halflings. 1:2 or smaller based on the Human proportions would work well in my view for the Halfling. Just with some Halfling fashion, some ear or hair flare to help set them apart.
Importantly the Halfling skulls should remain proportional with the rest of their body, and not be larger in relative terms - not even slightly larger, as that is the hallmark of a child in cartooning and will cause the confusion they should be trying to avoid. Having huge eyes and the like as well will only compound that impression even further.
If anything the ratio for Halfling models compared to Human models should be pushed even more extreme in the shorty direction. In other words having a Halfling model that is totally proportional compared to a Human or Half-Elf, but even shorter than the 3 ft tall height suggested many times in this thread - say closer to 24 inches rather than 36 inches (thigh high or even knee high, rather than waist high, when standing next to a normal Human). Then it would be impossible to confuse a Halfling with a kid.
This is also an instance where I would ere on the side of giving the Halflings body types that are very obviously sexually mature adults, with very adult anatomy and facial morphology - again to avoid any confusion with an adolescent Human. There are things they can do to make that clear, and to be particularly careful, by really making sure the Halflings all look more like 25-year-olds rather than 15-year-olds, if that makes sense. I'd avoid anime as a stylistic choice for the facial morphology, because it drifts pretty far in the other direction.
Larian's choice to make this game so sexually explicit does present some problems, but rather than worrying about whether our Halflings can properly bang Minthara in full HD, I'd rather they just had a shorty cut-away or fade to black for anything that doesn't work. I mean do we really need to see it? It'd also be just as easy to have a sexy Halfling or Goblin NPC at the Camp Party, who gives Halfling PCs a chance to get their rocks off, without causing people to have a heart attack if it's ever posted as a meme or whatever. They should just steer clear of anything even remotely questionable with that, and when in doubt, just cut away.
Right now the Halflings all look whack attack in my view. I don't want to play any of those models as a PC, and since there are no shorty companions, it just relegates the race to NPCs as far as I'm concerned, which is a shame.