First of all, I don't think the kid is an issue here. Obviously the infant had ridden the ride and had not suffered any harm. The only reason the kid is at all an issue here is because it would have made it more difficult for the person involved to safely exit the boat. But the same could be said for any item she might have been carrying...camera, purse, picnic basket, infant kid, whatever.
Second, PotC is a flume ride. As such, I'm guessing it uses typical weir brakes in the loading area...if the boat did lurch, it was probably struck by another boat, or the shifting passenger load allowed it to move forward on the brake roller slightly. Either way, it was not necessarily any kind of failure, and it was not necessarily anything that could have been prevented given the design of the ride.
I do get the impression, though, that this particular person may be overreacting to the incident. A lot of things seem fishy here...
--Dave Althoff, Jr.