I am trying really hard not to laugh because I thought maybe this thread was about kids my kids' ages and then read it and saw it was about much younger kids and then thought, wow, I'm sure glad my kids are past that age and then realized how many more years of arguing the OP had ahead of her which just sort of tickled my funny bone.

I asked the kids if they would like me to take them out to lunch today and they immediately started trying to negotiate for something better so they had to make their own sandwiches instead. (I don't negotiate. When they try to take advantage of my generosity I withdraw it because they started trying the same tactics on my dad and I was mortified and am trying to teach them about accepting or declining graciously right now.)
Yes, they argue and try to negotiate for many many years. On the upside, you develop a sad but useful ability to ignore it and blow it off. I swear it gets easier but am not sure whether that is because they argue less ir because you just get used to it. Also, if you make a policy of never negotiating once they start arguing, they start to give up much more amicably and suggest and accept compromises more politely after a while.
You definitely have my sympathy.