They're also supposed to be in them until they're 10 or so, these days. You're likely to go through 3-4 seats per kid—infant (often also a carrier), toddler, then either a larger car seat and later a booster or a convertible booster that can do both.
And yeah, you absolutely hand them down to younger kids. Throwing out old car seats is nuts and not something people actually do unless 1) they have more money than you know what to do with, or 2) the seat looks like it's in bad shape or reveals on inspection that it's damaged or deteriorating, or 3) you just don't know anyone who could use it.
And yeah, you absolutely hand them down to younger kids. Throwing out old car seats is nuts and not something people actually do unless 1) they have more money than you know what to do with, or 2) the seat looks like it's in bad shape or reveals on inspection that it's damaged or deteriorating, or 3) you just don't know anyone who could use it.