Rather than laws that limit the amount of children someone can have, I think that birth control should be encouraged, free and readily available. Especially in areas where abortion is discouraged or illegal.
The child policy in China has resulted in gender-selective abortion and infanticide as I'm sure everyone's aware, I believe there was something like 115 boys per 100 girls born in 2010. I don't think it's the correct thing to be doing.
People shouldn't have their right to reproduce taken away, especially if it forces abortions or sterilization, they are invasive surgeries.
Gentle encouragement to use birth control and awareness of the overpopulation would be helpful. And free birth control should just be the law everywhere, in my opinion.