Yeah, so the plants turn carbon dioxide and water into cellulose and water mostly, herbivores digest the cellulose into protein and carbohydrates we can eat, we eat them and turn that protein and carbohydrates into our bodies and energy using oxygen, back into carbon dioxide and water and expel it. It's the carbon cycle.
When plants undergo photosynthesis, they break the oxygen off the CO2 molecule and create carbohydrates. At this point, the CO2 molecule ceases to be. So to say that there is CO2 in food is incorrect. Our bodies recreate the CO2 when recovering energy from those carbohydrates.
I said food was made from carbon dioxide and water, and repeatedly explained the process I was referring to. I never once said carbon dioxide was "in" food, although even if I did I don't think it is this easy to misunderstand what I'm saying.
Apart from the babies thing, that's still a very interesting question. I bet someone knows the answer, but I wonder if the weight of the earth increases or decreases on average. I'd have to guess it's a net increase from picking up stuff as we move through space, which probably dwarfs the mass of stuff we've sent out (especially if you don't count satellites since they're more or less still tied to earth). I don't think there's anything like natural ejections of matter from earth either.