However, if an individual person starts making noise or moving erratically the animal can distinguish them and can attack. That is why many of the safari services will not allow kids under 12 or they will give groups with younger kids a very different safari to avoid dangerous situations.
As for being in the open top vehicles... there is no better way to see these animals in the parks. Being an arm's length from the animals is thrilling and getting an up close view of them is incredible. I cannot wait to be able to afford a return trip.