My 18 month old DS goes to a childminder 2 mornings a week (shortly rising to every morning). Initially car seats weren't an issue as the CM had 3 little ones and couldn't fit three baby seats in the car, but now DS is there on different days she is doing some driving with him. I have never seen her car/carseats as I don't do any drop offs or pick ups, but DP says they seem "fine" - we don't have a car ourselves though so don't know much about carseats.
Another mum who uses the same CM asked me the other day if I was happy with the car seat arrangement, as the seat DS uses is apparently very old and shabby looking (this mum's child is a little older/bigger than DS and is in a high-backed booster type seat that lasts from 12 months to 11ish I believe).
DS is quite small (about 10kg) and we have been using a rear facing baby seat from a travel system for the few occasions when we use a car, but he is now outgrowing it and we are thinking of getting a bigger forward facing seat - would it be reasonable to ask the CM to use our seat? We'd be happy to leave it in her car all week if she needed to use it in the afternoons.