My mother and grandmother tried very hard to "break me" of trains.
I was punished for mentioning or even playing with trains for a few years.
It did not work. I have branched off from HO scale, I now run N, HO, S, O, G, and 8 3/4" (Ride on train set).
And about the other gender, well, I have got my wife hooked on trains as well.
You can't beat a child into not liking trains. (such was the case with my mother, there is a fair police record of that) I would advise trying to steer the direction that the collection goes in if that is how you feel it should be done, but there is nothing wrong with multiple scales.