To me it is a "lesser of two evils" situation. When my kids are in their seats, the buckles aren't even able to touch them, let alone go in their mouths. Is lead absorbed through touch? I'd rather keep them safe from thousands of lbs of speeding vehicles on the roadway than obsess over chemicals. not using a car seat as a stand against chemicals is cutting off your nose to spite your face.
Mom to a girl - 6, a boy - 4, and Baby - 2