We should start encouraging smaller families in America.
But requiring only one child by law, as in China, is repugnant to USA sensibilities as it should be.
However, allowing only 1 child dependent deduction in our federal taxes would slowly ingrain in American minds that having a smaller family is the correct long term solution.
ALSO, No other benefit provided by US government should allow more to be given to a person or family due to having more children.