6 year old kissing and boyfriends- help and tips!

my 6 year old step daughter has increasingly been mentioning boyfriends over the past year. we tell her that she can tell us anything and she can have friendships with boys but no real boyfriends because that's something saved for grown ups. she just wrote a letter to a boy today (pretend letter) that said she wanted this boy to break up with her friend because she loves him and wants him to kiss her on the lips and marry him. this was right before bed and I told her that there was a few things wrong with what she's feeling and I won't go too in depth with what I said verbatim but then I said her and I would talk more in the morning. can anybody give me any tips on how to handle this? I also don't want to say the wrong and then her not trust me and be sneaky either!