Family planning

What is the Optimum Age to Have Kids?

Salaam… What is the optimum age to have kids. I am reaching 40 and I have had 2 children with operations. Should I go for more kids? Is it haram to have contraception? Why is it haram? I did not have a permanent operation and neither am I considering it. The contraception method my husband uses has worked for us so far, so I want to keep continuing with that. My husband and I are financially stable for now al hamdu Lillah, so far; but the way economy is going, that can't be for sure. We live in such a condition that we both have to work to run our family. If we have more children, I'd have to take a break. It would have to be short, and then I would have to go back to work soon. Which means the baby, like my other children, would have to go into day care. Is it fair on the little ones to go into day care? Now my kids are old enough, and going to school. They are requesting us to have another baby because all their friends have. They too want a little one to play with. I feel guilty that I am not having any more. I am afraid because of a number of things. My job, the economy and my husband's job, my age, etc... In my family, I have 1 sibling who is mentally ill. I strongly suspect [another sibling is likely to be mentally ill]. My father probably had a mental problem towards the end of his life. My children, so far are healthy al hamdu Lillah. But with age,. I am becoming more insecure in terms of mental health for my children. Is it advisable for me to still have more children? Why does Islam encourage to keep having children. It is not unfair to the child that its parents will not be young enough or not live that long when they need the most (during their wedding years or higher education). When I look around, the more children a family has, the less they can provide for higher education or other facilities. Especially here in the U.S., it is so difficult to raise kids in an Islamic atmosphere. My two children go to a private Islamic school. It is also very expensive for us and like I said, I'd have to keep working. So, even if I have to still send the baby to day care does Islam encourage me to still keep having children? What is the reasoning?