Consider the following dialogue:
"How are you, Juliet?"
"Ohnot too bad"
The child has evidently heard people saying responding to "How are you?" with "Oh, not too bad" and has come to learn "Ohnot" as though it is a single word. Is there a term for this sort of error, whereby two (or more) words are mistakenly learned as though they are one?
The first word needn't have been "Oh". I've seen this error occur with more meaningful initial words.
It's rather like a mondegreen or malapropism or eggcorn, but different in that the end result isn't a word at all.