I never did know very much about Andrew Gold, but I always wonder what his parents and sister (and brother-in-law, and nephew) thought about this.
He always denied that the song was autoobiographical, but given the coincidences between the lyrics and his own family situation, it must have been tough for them to take. The one element of the words that backs up Gold's claim is the idea that a two year old boy can feel neglected at the birth of his sister. No two year old would a) react like that; b) understand the explanation; or c) remember it afterwards.
He was great, Andrew Gold. That he died just a few weeks before his 60th birthday adds to the tragedy. As for his other big solo hit in the UK, well, some songs are best left well alone, aren't they?