Proto-Halfling language

Proto-Halfling was the ancestor of the Halfling languages. Since the Halfling language is quite conservative in its grammar, and hasn't had too many sound shifts in the last millenium, it is difficult to exactly pinpoint where does Proto-Halfling end and a form of Halfling that could be described as "close enough to the contemporary" begin, although the definite point of transition is usually put at the 9th century BEKE, when the proto-language fragmented into clearly recognizeable dialects that still remain mutually intelligible to this day.

Earlier developments
When Proto-Halfling and Old Dwarven weren't developed yet, but were instead still diverging dialects of Proto-Norlokian, some developments - especially in the articulation of vowels - were already starting to set the two future languages apart:

Developments in Early Proto-Halfling

 * The labio-palatal unrounded to.
 * The distinction between the sibilant fricatives and affricates  shifted towards a distinction between postalveolar  and alveolar . They would be realized as affricates word-initially, after nasals and when geminated, fricatives otherwise.
 * All of the plosives developed lenited allophones  in postvocalic positions, but only when ungeminated.
 * The flaps became trills  when word-initial or geminated.
 * The schwa became silent, unless it would have created a consonant cluster larger than three consonants (or two word-initially), or word-initial plosive+plosive, nasal+plosive, nasal+sonorant, sonorant+plosive clusters. In other words, word-initially, only sibilant+plosive, sibilant+sonorant and plosive+sonorant clusters were allowed word-initially.
 * In contaxts where didn't become silent, it became  after slender consonants,  after broad consonants.
 * The long schwa - which developed from  after broad consonants - consistently became.
 * The glottal stop became silent. If it formed a consonant cluster with any other consonant, it put compensatory lengthening on it.
 * Vowel shifts:
 * Monophthongization: →
 * re-diphthongized to after broad consonants. This shift ensured that front vowels shall only appear after slender consonants.
 * This vowel shift also made a special kind of broad consonant that also appears before front vowels. It also gave  a special role of being able to appear between a broad consonant and a front vowel.
 * A-fronting:

Early Proto-Halfling

 * was - and still is - a special kind of broad consonant that, unlike other broad consonants, can be followed by both front and back vowels. It also served as a prosthetic consonant between broad consonants and front vowels.

The Transition
The consonantal system of Early Proto-Halfling was not very stable. One of its more fragile elements was the allophony between plosives and fricatives, especially sibilant affricates and their fricative counterparts.

First, the sibilant affricates lenited to regular fricatives before any consonant - even in word-initial clusters. Inconsistent and unsystematic removal of word-initial short vowels in some very commonly used words, as well as prolonged contact with languages that contained word-initial fricatives: namnely, Archaic High Elven and Proto-Human. This cemented the status of those fricatives as separate phonemes from their plosive counterparts. Their voiced counterparts never became separate phonemes.

Late Proto-Halfling

 * was - and still is - a special kind of broad consonant that, unlike other broad consonants, can be followed by both front and back vowels. It also served as a prosthetic consonant between broad consonants and front vowels.
 * All variants of Halfling eventually lost the voiceless dental fricates, but Eastern Halfling variants would eventually regain them, mainly from loanwords from Old Etrandish and Dwarven. Nevertheless, before their reintroduction to Eastern Halfling, this happened to the voicelss dental fricatives in Halfling:
 * Some variants would harden back to
 * Some variants would debuccalize to  - in other words,
 * Some variants would glottalize to, reintroducing that previously-lost sound
 * Some variants would just straight-up make silent, optionally with the transitional period of  →  → Zero (linguistics), but some variants made the transition to null directly.
 * All variants of Halfling eventually merged into  (making it a special kind of broad consonant like ), and shifted it to uvular.

Unlike Eastern Halfling, Western Halfling would never regain the voiceless dental fricatives, because rather than Dwarven and Etrandish, it was instead heavily influenced by High Elven, which lacked dental fricatives.

Vowels
Unlike the consonantal system of Proto-Halfling, the vowel system was rather stable and didn't really change during the course of the language.