That’s the foundation of ad hominem. It doesn’t matter whether a two year who knows nothing or an expert with a life of experience says “climate change is happening”, because the expertise of the person making the statement has no bearing on the truth of the statement itself. The two year old who can barely think is still right, even though he’s not an expert, and if you want to debate it then you have to debate whether climate change is happening, not whether the two year old knows anything.