GMC 2004 Sierra - Manual (Page 42)

Every time infants and young children ride in vehicles,
they should have the protection provided by appropriate
restraints. Young children should not use the vehicle’s
adult safety belts alone, unless there is no other choice.
Instead, they need to use a child restraint.
{ CAUTION:
People should never hold a baby in their arms
while riding in a vehicle. A baby doesn’t weigh
much -- until a crash. During a crash a baby
will become so heavy it is not possible to hold
it. For example, in a crash at only 25 mph
(40 km/h), a 12-lb. (5.5 kg) baby will suddenly
become a 240-lb. (110 kg) force on a person’s
arms. A baby should be secured in an
appropriate restraint.
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