5e doesn't give any specific physical descriptions of anatomy or anatomical details that differentiate halflings from humans - such things are usually mentioned if present in the race description - aside from their overall size. The official art varies by individual artist art style, but the *greater majority* of it shows figures that are more or less human proportioned in most ways; individual instances of ridiculously tapering extremities and balloon heads are the trait of a particular artist, and their particular art style, and are not indicative of the majority of other official art representations (it's just unfortunate that said artist was used for the splash image on the halfling's own phb race page). The majority official arts we have since 5e shows human-proportioned halflings, with relatively uniform scale, very *slightly* larger heads relative to shoulder width than you'd expect on an adult human, and slightly stockier dimensions from knee to toe, as you might expect on a smaller creature.
The elongated head trait that was common in 3.5 art didn't seem to come forward in any official 5e artworks, but the crux of it remains that in 5e we didn't get any strong physical descriptors other than their overall size, that created any definite physical differences between them and humans... so we have a spread of different artists who all made official art in their own style and vision, but none of it truly definitive. the most common depiction, by number of official representations, is as more or less down-scaled humans with the minor differences I mentioned above.
