I totally understand how this triggers questions inside ourselves as moms. These days, I get, "I want to be a famous singer.". And I don't want to be the dream-squelcher, but that's a tough dream. So I nod and say, what would make you happy about that? And maybe your could sing for smaller audiences, too?
I'm not trying to dissuade her, just to see a bigger connection, that the dream can change and still be rewarding. I like to think that he'll get to enjoy the fun of soccer for years and years. :)