Here's the problem? There are other problems than you mention such as breaking the rules they have in place for a purpose. The F cabin on AF is advertised as a quiet oasis away from it all. A screaming infant on a lap? Isn't that a problem? Maybe not for you, but for the person paying $10,000 one way for F it could be a big problem. Why shouldn't AF protect them?
Did you book the RT through Delta and they are including the infant in the record? Isn't Delta breaking the AF rule if that is the case? Or, maybe the infant isn't confirmed at all and you have no ticket for it. In that case wouldn't the infant be considered a stow away and not even listed on the fight manifest if AF allowed it to board without a ticket? Worrying about this the whole trip could spoil the trip. I would vote for taking care of the problem before leaving on the trip.