This is pretty disgusting, and I'm not talking about excrement. Whoever wrote this did so with malice aforethought.
First off, it presents a scenario designed to provoke one's protective instincts - an adult male striking up a conversation with a little girl he doesn't know. So already the reader is subtly encouraged to support and defend the little girl's side.
Second, it has him talking about a really weighty subject, the existence of God and heaven/hell with her, although she's presumably not knowledgeable about it. So it sets up the atheist as a smug bully who's picking on a poor little girl. There's also a possible stalker vibe there, though I'm not as sure about that.
Third, the stupid excrement joke, which plays on both of the points I mentioned previously to have the little girl show up the atheist and make the reader feel proud of her for putting the atheist in his place.
In short, this meme is a subtle, well-crafted, malicious one that's designed to present atheists as pathetic bullies who can't even successfully convince a (supposedly) impressionable little girl of their point of view.
So, responses. One is to ask the person if they think that atheists stalk random children they don't know, as this meme suggests - instead of trying to rebut the meme, counter it. It's a little aggressive, but on the other hand, I suspect that most people won't have thought over this meme to realize how insidious it is.
Another is to point out the falseness of this meme - that atheists don't approach random strangers (especially strange children) to preach 'doctrine' at them, etc.
A third is to compare and contrast actual atheist behavior with actual Christian behavior - for example, that evangelical Christians present their beliefs as fact to children that they don't know very well, if at all, whereas atheists tend to only discuss things like this with people who initiate it with them.
Or combine them somehow.