Don't get upset with me, but I think your counselor was onto something, just worded it horribly. I don't think it was meant as a good fantasy, no of course you don't want to think of children in that way, but consider the existence of a negative fantasy. Just like how you can have good dreams and nightmares with the umbrella term "dreams". I think what she mean to say is that this is somewhat of a self fulfilling prophesy. Such as, you are always afraid of thinking becoming a pedophile, so when you're subconscious is left alone, it remember whatever frequent thought you had. It doesn't pick up on the negative connotations you think of it with, it just takes the person/place/thing as it is.

My phobia is very different from your (needles) so I don't know if this will help any. If you get an image that invades what you planned to fantasize about, can you say to yourself "ok, that's not what I want" and replace it with a new image? I think by refraining/fighting, it's on your mind more (again, I'm not saying on your mind in a good way) which puts the image there. Also, I'm not a doctor by any sense, but to me (and my limited experience) this almost sort of sounds like OCD? Or pure O because there is no compulsion behind it? Maybe some of the therapies for that would help you from obsessing about your fear.

Can you try to focus on the ways in which you do/want to interact with children. Focus on the healthy behaviours. Curiosity, does this lead you to avoid contact with children? Are you afraid you would hurt a woman if you were in a relationship with her, thus avoiding the area all together?