The risks of second hand shoes:
They are already worn. It takes a VERY short time for the shoe to mould to a foot. You wear a pre-worn shoe and it contorts your foot into that shape, which can be painful. As babies' feet are still changing so much it can push the bones into positions that will last the rest of their lives and need operations on in the future.
A carseat may not have seen and accident and you may not have one, so that can be immaterial. An old shoe WILL cause untold damage to your child - take it from someone who has had her feet damaged by bad and old shoes.
eta: we only play on the grass barefoot and I go out and pick up all the holly leaves first! But DS will happily run over stones barefoot and all I can do is follow sometimes - his feet are REALLY tough.

