It is not necessarily that he wants to have sex with little girls, but it may be that there is something erotic in the pigtails for him. There are a range of fetishes, you are correct, and often these involve a very narrow aspect (e.g. feet alone, or underwear, or type of material, etc.) I am wondering if he is wanting you to be childlike in other ways too; creating more of a picture of sexual interest in young girls, rather than just one aspect of it?