Someone sees Harry being nice to some random kid - buying them ice cream after they scrape their knee or something - and finds it cute. The kid's mom is acting all flirty with him, and Harry's oblivious of course, since he's focused on the kid.
So the Someone Watching decides to come over and make it obvious that Harry belongs to them. With or without Harry noticing, up to you.
Random Acts of Kindness
Someone sees Harry being nice to some random kid - buying them ice cream after they scrape their knee or something - and finds it cute. The kid's mom is acting all flirty with him, and Harry's oblivious of course, since he's focused on the kid.
So the Someone Watching decides to come over and make it obvious that Harry belongs to them. With or without Harry noticing, up to you.