I believe you could say that these words are phon(a)esthemic.1 Several2 of the words you are describing feature a phon(a)estheme3 which contributes to your sense that their meaning is somehow reflected in their sound. From Merriam-Webster:
Definition of phonestheme
the common feature of sound occurring in a group of symbolic words
- He points to a 1929 experiment by Edward Sapir in which Sapir's subjects were asked to match nonsense words with small and large versions of the same object. The subjects tended to match words with a high vowel (such as ee) to the small object and those with a low vowel (such as the o in "cot") to the larger object. British linguist J.R. Firth later called these links between sound and meaning "phonesthemes." —Michael Erard
A ThoughtCo article by Richard Nordquist offers a more straightforward definition:
A phonestheme is a particular sound or sound sequence that (at least in a general way) suggests a certain meaning. The adjective form is phonesthemic.
So you could say
"The word Twinkle is phon(a)esthemic because [it contains sounds that are associated with sudden or repetitive motion and smallness, so it] sounds sparkly and light when spoken which is appropriate to its meaning, but not directly connected"
1 For those who still aren't sure about this phenomenon, Terry Pratchett explains it better than I can (though it seems he wasn't aware of any common word for it):
Glint, glisten, glitter, gleam...
Tiffany thought a lot about words, in the long hours of churning butter. 'Onomatopoeic', she'd discovered in the dictionary, meant words that sounded like the noise of the thing they were describing, like 'cuckoo'. But she thought there should be a word meaning 'a word that sounds like the noise a thing would make if that thing made a noise even though, actually, it doesn't, but would if it did.'
Glint, for example. If light made a noise as it reflected off a distant window, it'd go 'glint!' And the light of tinsel, all those little glints chiming together, would make a noise like 'glitterglitter'. 'Gleam' was a clean, smooth noise from a surface that intended to shine all day. And 'glisten' was the soft, almost greasy sound of something rich and oily.
2 Wikipedia includes sludge in its examples of phonesthemic words (sl- words are one of the classic English phonestheme examples, along with gl-; sl- words are often pejorative and/or slippery, and sludge fits both), and twinkle also appears on some lists (both for the tw- start and -le end). Splash does have onomatopoeic features, but it also appears on lists with other liquidy spl- words like splat and splutter. I'm not sure whether bell contains any phonesthemic features.
3 These sounds are also sometimes called sub-morphemes (because they seem to carry some meaning even though they don't reach the level of a morpheme) or word-affinities. They are related to ideophones and fall under the more general heading of sound symbolism/phon(a)esthesia/phonosemantics, an area of expertise for EL&U's own John Lawler. There seems to be a continuing debate about whether the "meaning" that attaches to the various sounds is always language-specific (some dictionaries specifically define the phenomenon as a result of having a large number of related words in a language that share the sound) or if there is some inherent, universal connection between some of the sounds and human perception of their connotations, but either way I believe this describes the experience described in the question.