Indeed domestic flights had a different system from European as they are mono-class. But I think that it can have changed with the NEO concept. In any case, I do NOT think that you can prereserve seats on a domestic flight.
My experience, as well as the recent and extensive experience of my children (who are parents), is that AF blocks a row (with double oxygen masks) for family with infants. So the seats are not "reserved" but preassigned (blocked). There can be many infants on a domestic flight; I would assume that they choose the row as a function of status, just like they do at OLCI for normal pax. But all the experience is pre-NEO, I will learn more this week.
Creber, were you unhappy with the row you ended up with?