Originally Posted by pptp

I don't want to be an alarmist or infer that flying isn't safe, because it is, but there are very rare occasions where clear air turbulence (CAT) does occur. If it does, you could experience negative G's (your cup comes off the tray table). If it hits -1g, it would be like someone holding you against the ceiling of the aircraft then letting you free-fall to the floor, except with CAT, once you go up, you have to come down again. Of course the thought of this happening to a baby is nightmarish.

The occurrence of an extreme event like that would be very rare and therefore a pretty safe bet but it's definitely something a parent should consider. That's why the pilots keep their lap belts on at all times and CO policy is that PAX keep it fastened at all times too -- this would apply to infants as well.