How tf. is it making a child into an activist?
"You have an issue you feel uncomfortable about, and feel your safety is threatened? let's talk with a democratic representative, so they better understand you." Is not "activism". It is normal political process in a democracy and it should be endorsed, especially for children. They have rights too and they have opinions too and since they cannot voice their opinion in elections it is all the more important that they can be heard by politicians. And there the bar is also different. A child cannot be expected to form a conscise political argument, leave alone lobby for it, what would be activism. But children have legitimate concerns that need to be heard nonetheless.
By this definition raising any issue with any politician is "activism". Also who the fuck would deny a child to change its mind as it grows up?
The difference here is that children often lack a concept of sexuality, because they don't feel sexual attraction yet. That liking someone or being attracted to someone is two different things, is something children usually learn in puberty.
But children very well understand, the social constructs we create for boys and girls, and can express whether they feel that fitting them or not.
Finally you said:
This is exactly what the issue is about. Let the children use the bathroom they feel most comfortable with and not impose a gender and sexuality on them.