Is it wrong that I I don't want my fiance to create a YouTube channel or vlog with our kids in it?
What makes you uncomfortable about your fiance making a YouTube channel with your kids and it??
I want to show the world how our kids are growing without using social media.
It's understandable that you don't want to expose your children to an online environment. Having this concern for your children is to be expected, you should talk with your fiance to find alternative ways that show people how your children are growing. If you outright deny your fiance what she wants, this could upset her greatly and cause issues in your relationship.
Just because you disagree with something, doesn't mean you should try to control what someone else is doing.
I agree and I think you got the point. I would be a little concerned too about my child being on social media and I'm sure you will find a way to work this out.