Our food supplies have been getting more secure for centuries, and we've seen no meaningful selection pressure towards larger families as a result - quite the opposite, in fact. And this isn't a millions-of-years sort of selection, this is the sort that ought to be apparent in a few generations. I don't think that number of children is really a heritable trait - it's a cultural and economic effect, and even if you start speaking of cultural evolution, the economics of having lots of kids are so bad today that there's no selection pressure in that direction.

In principle you're probably right, but by the time we need to worry about Malthus again, the name "Malthus" may well be forgotten.