That's where things like the cashback initiative comes in:
https://www.sufc.co.uk/news/2019/july/united-cashback-initiative/ (they're the kids you see dicking about on the pitch at half time).
I think there's two separate strands going on in this thread.
How do we attract local kids to Bramall Lane to be Sheffield United fans for the future? - a cause I'm greatly sympathetic to.
And
How can we serve Premier League football fans who aren't necessarily going to become Blades but just fancy seeing a one-off game? - a cause I'm rather less concerned about.
None of us were weaned on the behemoth that is the Premier League, where club loyalties are less of an importance than the spectacle of the product- where it doesn't matter what match you go to because you're watching "the Premier League". Bramall Lane would become a far different place if our main priority was to fill it with day-trippers.
As an example, I've offered in a local interest group that if tickets are ever opened up to ST holders, members can give me a shout and I'll try and sort them out so their kids can get on the ladder. I immediately got a message saying "I will take you up on this for Spurs because my son really wants to see them on his birthday". Now, it's unlikely that Spurs will be one of the games opened up for ST holders to buy extras, which I did point out. But should I potentially deprive Blades from seeing the game because some young local lad wants to watch Spurs?
This is where the loyalty points scheme is right and fair.