Limit the Number of Children Covered under Welfare Benefits

In order to help reduce future federal spending and promote a more responsible nation, I propose that families receiving Welfare shall not receive benefits for children born after the second child. This should only apply to children born after the bill has been passed in order to avoid potential economic disruption.
If a family is in need of federal assistance there is no reason why they should raise an above average sized household. If they cannot normally afford to support 3+ children (through employment or other income), why should the federal government? Limiting Welfare's additional benefits to 2 children would save taxpayer dollars and promote responsible family planning.