Epenthesis is the insertion of a consonant or vowel, usually to ease pronunciation, as in the p-sound most speakers use in ham[p]ster, or for those who find thl a bother to pronounce, the insertion of a schwa in ath[e]lete.
Now your particular case is somewhat different, since retaining a vowel otherwise elided is not the same as inserting it where it never was to begin with. It could be argued that in the present participles – or other derivatives such as agent nouns in -er – derived from verbs ending in -le, the elision is very common, but not mandatory. While most native speakers would pronounce toddler with the elision, toddling sounds more natural to me without it. At any rate, I don't think the non-elided form of such words is so deprecated that it would be considered an error. In other words, a matter of opinion.
A similar case is the tendency of some native speakers not to pronounce vocalic n in contractions such as didn't, wouldn't, or couldn't, instead inserting a schwa or lately even a fronted vowel before the n, or in words ending in -ant where vocalic n would otherwise be expected, like important. (Take that, Ezra Klein! See this video at 1:40 mark) While this particular pronunciation puts my teeth on edge, enough educated elites use it in their podcasts that calling it an error rather than a new variation seems ill-advised.