I always try to teach the science and ask them to come to me with questions.

Just about any biblical story makes no sense if taken as a fact (and not a parable), I think you could take your pick.

Try asking: Can God do anything? Yes. Ok

Can God make anything? Yes. Ok

Can God make a stone? Yes. Ok

Can God make a rock? Yes. Ok

Can God make a boulder? Yes. Ok

Can God make a mountain? Yes. Ok

Can God make a mountain so big that he himself couldn’t move it? Yes. Ok

If God can do anything can’t he move the mountain he just made? So him God? Hmmm

Easy ones I gave my 6 year old son.

Who is God?
What is God?
What does God look like?
What are angels?
What are demons?
Who created the angels and demons?

then follow up with:
How do you know?
How do they know?
First prove they exist, then we can try to figure out how they were created.

A simple line of questioning like this got my son to see the point.

Ask what you should do if god told you to sacrifice one of your children.

Okay, seriously. My son and I had multiple conversations and I did not convince him. I asked everytthing and nothing cracked his faith, but questioning the morality of various churches and ministers and pointing out the hypocrisy swayed his views.

He's still religious, but not hypocritical or judgmental. He doesn't preach or impose his beliefs on others. He's one of those rare liberal christians with a conscience. I'll call that a win.

Perhaps the story of noah,s ark.there is so much of it that makes no sense. How could so few people collect and take care of so many animals. How could they feed them. How could they keep them from killing each other. If evolution isn't true they had to collect every type of every species.how did they catch every type of bird on every continent. How could they build a boat that big with the same few people. How did they redistribute those animals. How did the plants of the world survive. There is so much more that's wrong with that story alone. How I handle that problem is to talk to them about evolution and answer questions with the factual truth. Time will do the rest. Either way mine decide at least they have time to decide for themselves and I hope the memories I left with them teach reason and science even if they ultimately believe in a god. That would be fine with me. Lots of people do

Get them into astronomy or take the to a natural history museum

What age is the child? This is an important consideration.
However, it is very easy to draw an analogy to Father Christmas, which is a lovely myth for young children to be fooled with - but which they eventually work out for themselves is just something which brings joy to youngsters, and then to question whether religious belief is not also perhaps a myth.

Not sure if you are familiar with the site, but atheist republic has a good list of books for skeptical children. Some of them will probably have stuff you can use in conversations.

[atheistrepublic.com]

What age?

How about an examination of the mythical stories about Santa Claus, the Easter Bunny, the Tooth Fairy, and the Great Pumpkin?