лепетать(о детях; To speak with imperfect articulation; to mispronounce, such as a child learning to talk); картавить; говорить запинаясь; сюсюкать(to speak imperfectly or like a child); шепелявить([OE wlyspian, of echoic orig.]; to substitute the sounds (th) and (th) for the sounds s and z, as in pronouncing sing as though it were thing; to say th for s or z because of being unable to pronounce these sounds correctly)
шепелявить(pronounce the consonant ‘s' imperfectly; to give ‘s' and ‘z' the sounds of ‘th' (/θ/, /ð/); a speech impediment common among children); пришепётывать(Liv Bliss)