My kids were kind of older when we got started. I think older DD was about 11 when she saved up the money for Kit. As soon as she arrived, younger DD (8 then) had her money out and counted to see how soon she could get one. (It was at that time I learned that my aunt had bought the other great-nieces their AG dolls, but since one DD had saved up the money, the other had to save hers up too.)
Some time in the last year, I found one at Goodwill that was sort of similar to DD11, so it became hers. Then DD14 decided she'd like one with longer hair than Kit's, so the girls pooled their money to buy Marie-Grace so they'd each have two.
They don't get a lot of play these days, but they do enjoy having them for sure. In our house Build-A-Bears have been the most played-with toy!