Articulation Point: Root Case

If the DFS root has $\geq 2$ children in the DFS tree, it is an articulation point. Why?

Each child represents a separate subtree. These subtrees are only connected through the root. Remove the root, and they become disconnected components. If the root has only $1$ child, it is not an articulation point. The entire graph is one connected tree below it, and removing the root leaves that tree (or a single vertex if $n=2$).