Are you saying they can't testify about wanting to live in a future where Montana doesn't greenlight every fossil fuel project without an environmental impact review?

Or are you saying they don't know what those words mean?

I think you can get a meaningful testimony from them (yes, "I like hiking, I like swimming in our local lakes, I want policies that protect our environment because I want to continue to be able to enjoy it" - nothing here seems incredible for a five year old to say)

You might ask "ok but why? Isn't the case well represented by older kids? Isn't it well funded?"

I have no inside knowledge of this, but if a five year old's older sibling is participating, they might want to too? Does that make their testimony more or less valid? It shouldn't