My MIL believes that we would not need expensive carseats if they made cars like they did in the old days She understands that we need to use them, but does not agree. Before DD1 was born she was so happy that she had found us a carseat. I assumed she meant on special somewhere, but no, it was an old one that had sat in someone's shed for years. We had to rush out and buy a seat before she tried to bring it over on the plane with her.
My MIL did the same thing when we were pg with Ds1. It was the oldest thing ever. Even back then I knew you couldn't use it.. We just told her straight up no we wouldn't be using the seat but thanks for the offer.. and the rare time she had our son we either just swapped cars or took the seat out and put it in hers..