I must say I think of Nadia (octomum) when I read this question.
Who are we to say how many children one person may have? Even limiting abusive and neglectant parents is risky enterprise (I'm thinking of all the genuinely wrongful convictions and executions as I say this).
There was an initiative in India years ago (they're set to overtake China soon) which involved compulsery sterilisation of men who were convicted of even minor offences (no train ticket), they also offered the procedure free to willing men - though most of the participants already had large families.
After a public uproar the initiative ceased. The Indian gov has spent a lot of time and energy on finding a solution. They have learned that the higher the education of women, the less inclined they to have large families. It is women who have little or no education who don't realise that there are other options.
On a lighter note...I'm reminded of a comment made by my (new) step-father who, like me, has three children. After an incident that occured many years ago, he will warn anyone who listens not to have more children than you do hands.
Holding two of his children by the hand and walking down a busy street, he saw the third child make a dash for the road. Having no other option, he stuck out his foot and watched her topple onto the footpath!!!