I have two sons, one aged seven the other five. My instinct was that I was only capable of being a somewhat decent parent to one child, which I was while having a pretty decent quality of life.
My wife lobbied for a second child and against my better judgment I agreed. It was a a mistake I regret daily. While I love my son, I am not able to cope with the demands. I hope people can learn from my experience and have the courage to listen to their instincts as I should have. I see friends with one child and their quality of life is so much better.
My point is trust your partner, if they say they don't want something, respect that. If you are the person being pressured, please stand up for yourself even if it means severe short term pain.