Firstly, it’s typically stereotype for kids to be anti-romantic. Secondly, when somebody shows how much they despise something, the exact opposite could actually be the case.
As for me, I love the romance between them, I’m very passionate about it. Once when I was still living at home, me and my parents watched a quiz show. Suddenly a video was shown with the "Can you feel" scene because the question had something to do with it, and immediately when I saw it, I was all: "Yuck, please switch channel, that is so pathetic", and so on. Why did I say that, when I actually love it? Because I was embarrassed about it.
So maybe the first thing that went through their heads when they heard they were going to be married, is to immediately show the other how disgusting they think it is. Because they are so embarrassed about maybe having a little crush on each other.
I could be dreaming, because I love to think that is the case. But it has a psychological explanation.[/quote]
I think that theory is very plausible,it most certainly holds water.

It's also possible that,while they were cubs,they obviously liked each other a lot,but not in a romantic way of course,cause while they were so young,they couldn't even understand how that works,nor why they would feel like that,one of the reasons why the reacted to Zazu's statement like they did.
But,as they grew older and matured,they have also began to realize how much they meant to each other and let's say fall in love on distance,even if they didn't see each other.
Even though Nala thought Simba was dead,but you get the point.