You certainly wouldn't want to learn the opinion of an anti-gay Christian activist about your parents.
Which still would be a valid christian opinion (afaik?) and if Nintendo allows expressing the one they invite the other, meaning putting children in the midst of a culture clash with no positive side because they don't act on sexual stereotypes yet anyway.
"Valid" opinion is all dependent on what they and how they say it. But it's largely gonna be harder for them to express their opinion without being inappropriate, harmful, or derogatory, from my experience. And those kind of messages, much like on this forum, aren't tolerated on Inkopolis, soooo....
This may come as a surprise to you, but kids are already in the middle of a culture clash. Everyone who can understand language is. Kids learn and emulate from those who raise them, and I was already in the middle of a political tug-of-war between my parents and my grandparents since I was a child. Parents are trying to influence their kids, kids influence each other. That's what growing up is, you experience and learn about the world, and while you ultimately make your own decision on it, the decisions you make are greatly influenced by those around you and what they think. Culture changes constantly, and there's
always a clash.
And there is a positive side. For one thing, orientation and gender identity isn't something that suddenly appears on the onset of puberty, although obviously children aren't sexual. Young childhood crushes are a thing, after all. On top of that, it's not like prepubescent kids are the only ones playing this game, either. People of all ages are playing this game, many of them teens or young adults in a situation where they could use some support when trying to come to terms with their identity of orientation.
And more importantly, "LGBT people exist, and that's okay" is clearly the positive side, because even if a kid isn't focused on their sexuality and identity, they will be once they do hit puberty, and for those who are gay , trans or genderfluid, it's better for them to experience an environment where they're welcome and accepted, and not be fearful or self-hating for who they are, and to create an environment where they're not mocked by those who are straight for their identity or orientation.
These are human beings with real feelings, who have done nothing wrong and have no control over their sexuality or identity. To treat them with respect as valid and equal individuals is something to strive for, because the alienation of LGBT individuals as strange, unusual, or worse has led to untold amounts of harm to LGBT individuals and is what's led to this situation in the first place.