car seats
if you're flying an aussie airline, the rules about car seats are set by CASA. only seats certified by certain bodies are acceptable, and they must have the appropriate decals. So you could have a brand new seat on which the approval decal has been removed, and it wont be allowed to fly.
I think the CARES restraint i linked to earlier was partly designed to combat this problem and also to save mum and or dad from lugging a car seat everywhere.