Finding a player in the team that he adores/admires is key.
I have Salah to thank. My son was just 4 years old when Salah signed for LFC and the immense hype around him (Salah) in the first two seasons was crucial for my son in becoming an LFC supporter.
Iāve been obsessed with LFC for as long as I can remember but my father, who is actually from Liverpool, never had any interest in football until I got into it. When he realised how important it was to me he took me and my mates all over the country to watch games.
My own son has no interest in football and I never pushed him towards it. His entire weekās mood is not determined by the outcome of a football match and I think that has probably made him a more well-rounded individual. We bonded over different things. He does appreciate how important it is to me so he knows to give me space if we lose and heās the first to congratulate me when we win. Also, a lifetime of playing video games developing ninja like reflexes and a job that involves sitting in front of a computer all day has made him an expert at picking up tickets off the site for me.
So I think the lessons Iāve learnt are to let those closest to you find their own interests simply by encouraging them in everything they do, appreciating there will be always be some aspects to them that you will never fully understand. Also let your kids play video games if you want to get tickets for the match.
For my daughter it was the critical cynical touch with Gini a player we could all agree wasnāt good enough.
Of course āweā started in the days of Gerrard (who is my momās all time favorite player as well even though she couldnāt give a flying fuck about football until someone critised Gerrard 
). A figure like Gerrard is a great help.
Girls I feel are in general different they like the confrontation. My daughter at rugby matches just didnāt want to go but criky did she go nuts when the āgeneralā broke out (big fight) particularly if her favorite player was involved (you know the handsome tough guy). She seemed always much more interested when we talked about Gini than Hendo or ManĆ©, like whatās the interest if thereās no controversy. 
Ha. Love it.
I have 5 kids and started them all off when they were new borns. Jerseys, baby grows, soothers, all manner of clothing. As they grow they saw my love for Liverpool and distain for certain other clubs. So in my instance it was an organic process that has been a part of them since day one.