Originally Posted by
TribalistMeathead
(see also: the fact that I scoured the "traveling with children" pages and didn't find a single reference to the fact that, when booking flights that include an infant ticket, you can pre-select any seat in Y for free, even when purchasing a Basic Economy ticket; I stumbled on that by doing a dummy booking)
I was wrong about this being an unadvertised benefit, I found this just now:
Under-advertised, maybe, but not unadvertised.