Heuristically, I agree with jkaufman and lmm, but I wonder if you can do something like a Fermi estimate of the impact of this decision? (Leaving your potential fuzzies out of it for now; after you estimate the impact, you can talk with people of the appropriate reference class to help you predict the level of fuzzies that you're likely to obtain or lose. Then, if the numbers are going in opposite directions, you can estimate how much you care about impact vs fuzzies to help make your decision.) Here are some factors you might want to estimate:

• Some measure of how much of your income is likely to go to charity. What fraction of the income that you have left over after maintaining quality of life for yourself, family, etc do you think you will contribute to charity? (To get an estimate of this, consider how much you are contributing.) Consider whether this fraction will remain the same if you have a child.
• Some measure of the effectiveness of your chosen charity per marginal dollar. If you want to remove this from the equation, you could just compare fuzzies vs dollars, but I don't think that would be as useful, since (money contributed to charity) is presumably not a terminal value for you.
• Some measure of the costs of raising a child (may need to do this seperately for adopting vs creating a new human; I have no idea whether there is a significant cost difference).
• Some measure of the opportunity cost of the time you spend raising the child. You'd need to think about how to evaluate this, since it's not accurate for most people to bill these as working hours.