Well, sometimes it doesn't stick. My son liked trains in his younger days, played lots of Thomas, and liked seeing steam in Colorado. But he has no interest at all now as a 21 year old. In fact, we took him with us to Colorado this summer and when asked what he wanted to do, the answer was "if you want to do trains, you're on your own". I think the beginning of the end was when i took him to ride the Texas State Railroad when he was about 10 and he said "dad, that was just tree after tree after tree". He still at least tolerated the Colorado trains then and admits he enjoyed the Loop "because it was short, the bridge was interesting, and the mine tour was fun".
Now for me growing up, my dad and i railfanned all the time, especially in Colorado. We hiked lots of abandoned lines as a family including the Alpine Tunnel, Haggerman Tunnel, and and even hiked from the Durango KOA North along the D&S all the way to Tank Creek and back. This was before the Bradshaw armed guards/patrols. And my dad and I still love to talk trains. I wish my son and I shared the interest, but he's a great guy otherwise so I'm still blessed.
Dave