Time to break out the parental discipline card. For a three-year-old, put him in a time out or something, and if it continues, start taking toys away or something. It's time to take more measures if just scolding him isn't working.

Women are naturally compassionate; men are naturally logical and dominant. This is the ultimate problem with single mothers, (which I can tell you most likely are), and this is why 11 out of the 12 past mass shooters have been raised by single mothers. Single mothers are not very good at punishing their children. They are too compassionate; too forgiving; too WEAK. They do not logically understand the limits of their children. They don't punish children enough. Having a 2 hour back-and-forth discussion with a 3 year old child on why he should not do something, is ridiculous and unacceptable. Children at that age are in what psychologists called the "hedonistic stage"; they do not understand right and wrong, except in an extremely limited sense, mainly determined by what benefits them or what causes them pain/discomfort/annoyance/inconvenience. Also, talking to them in a dialogue makes them feel equal to you in terms of knowledge/wisdom/input. They are NOT equal to you in those terms. They, as a human being, sure, are of equal worth- but YOU ARE THEIR *ELDER*. More importantly, you are their PARENT. What that means is, they not only SHOULD listen to you, they are OBLIGATED to listen to you and OBEY you. They are not to question you. It is to be understood you are wise and they are not, they are a child and you are the adult. Period. What should have happened is this: When your child said they wanted to poop on their younger brother, you should have said "No, you cannot poop on your younger brother. That is wrong. Your younger brother did not mean to poop on you, and he is way too young to know better. If you poop on him, you will be punished." If the 3 year old still did it anyway, you should have said "Go to the bathroom and wait there." Then you should have walked in and spanked him, and when he cried, you should have said "Why are you crying? I TOLD YOU that you would be punished. Why didn't you believe me or show me respect? Don't do it again."

I know a simple solution. Control your god damn kid.

Eye for eye, right? Sorry, OP. This is a hell of a story to tell though.

Maybe try putting a diaper on the four-month old.

I dont know why you would waste your time trying to convince a little kid of anything. 2 hours??? that seems quite excessive.

You don't spend hours explaining to a 3 year old. I should think that by now you've taught him what no means??