Though I would love to have more children than two, I remain committed to not having anymore with her. I completely agree that that could go very, very badly, and I'm certain it would lead to regret on my end (and anger on hers).
As much as we wish having more children could be a positive in a marriage, we also have to be aware that if the marriage does fail then having more children would make the divorce even more complicated and difficult.
For example, right now your youngest will soon start grade school. If you had more children then there would be more years with babies, toddlers or preschoolers and you'd find it stressful to separate then. At least now, your kids have school or daycare as a regular part of their lives and they'll not be considered quite so dependent on their mother as would small children.