i think that if you start them young, 4 or 5 they will always like it. When they get older, 12 13 they start thinking about other things, hanging with friends, playing video games. then high school and women are on there minds. Once they get by that stage i htink most kids start to do things that are fun to them again.
People go through phases in life. Fishing may or not fit into your life, key is let it be his/her decisoon
Cheers!