LALLATION
babble, babbling, lallation
(noun) gibberish resembling the sounds of a baby
lallation
(noun) defective articulation of the ‘l’ phoneme or the phoneme ‘r’ is pronounced as ‘l’
Source: WordNet® 3.1
Noun
lallation (countable and uncountable, plural lallations)
The incorrect pronunciation of the letter "r" so that it sounds like an "l" (or "w").
Baby-talk or gibberish.
Source: Wiktionary
Lal*la"tion, n. Etym: [L. lallare to sing lalla, or lullaby: cf. F.
lallation.]
Definition: An imperfect enunciation of the letter r, in which it sounds
like l.
Source: Webster’s Unabridged Dictionary 1913 Edition