Only the body is ten months old.
That "I am" seen here inside the eyes of a baby body, is exactly and wholly the same "I am" that will be in the adult body three decades hence. That internal still-witness-center-of-being observes (so to speak) the changes around.
A baby lacks nothing except a collection of experiences and named memories that will some day be misidentified as the "I am".
And who is to say, or prove, that the new born "I am" doesn't arrive already with a bag of impressions from previous emotions, preferences and memories.