Ideally during/after boarding but occasionally this doesn’t happen for one or two reasons and yes, cabin crew do occasionally miss them out until they do their cabin secure check. Just politely remind them, chances are they will already know you are there.
The cabin is classed as unsecure until the cabin secure check is passed on (indeed, a number of passengers will likely be unsecured at this stage) and as long as the baby is secure by this point then they are set for take off.