The other day, on our drive home, my eldest spoke up about his day:
Eldest: We went and saw the -th-grade play today. It was about a blue god with a big beard.
Me: Do you know which god it was?
Eldest: No. I only saw it once. (pause for a second or two) How many god’s are there mommy?
Me: It really depends on which religion you follow. Christians, Muslims, and Jews all have one god. The ancient Greeks and Romans had many. Different religious traditions have different views of god and gods.
Eldest: How many gods do we have?
Me: How many would you like?
The little one, who has been listening to this, pipes up: ZERO!
Eldest: One. The blue one with the big beard.
Little one continues to chant: ZERO!
Me: That’s fine, you can have one, or none, or as many as you like.
The eldest seemed okay with this answer. The little one seemed pleased too. Then they started talking about farts. Because, farts.
How do you handle these questions?
kind-ism 
The reason that Mrs. Eddy didn’t include impersonal Principle as a Bible Lesson is that Principle isn’t in the Bible. Principle is Mrs. Eddy’s contribution for the distant future to have a working definition of God that will be complimentary to the scientific age. My advice would be to explain that things that have action and reality all have a Principle in operation behind them. Without a Principle, a car engine, this Internet conversation, or the organization of the human body wouldn’t happen.
I’m going to stick with my answer, they can have as many (or as few) God(s) as they’d like. Principle has very little to do with gods with big blue beards.
Also, I was about to argue that MBE did list Principle as a Bible Lesson, and then double checked the list… it is one of her 7 synonyms, and most of the others are Bible Lessons.
Trying to think of how I would answer. It probably would go somewhere along these lines…
“No one really knows, it’s a great mystery. Some think there are none at all, some think there’s only one, some think there are many! What do you think?”