How to find if a child node of a binary radix tree is an internal node or leaf node?

Question

I am creating a binary radix tree(longest common prefix tree). The data is stored only in leaf nodes. The tree hierarchy has internal nodes and each internal node has two child nodes. A child node can either be a leaf node or internal node. Both leaf nodes and internal nodes store a reference to parent node.

Leaf nodes are stored in an array. internal nodes are stored in another array. Root node is first element of internal node array

Node
{ 
    Node* parent;
}

LNode: Node
{
  data;
}

INode: Node
{
    Node* leftchild;
    Node* rightchild;
}

Assuming that the tree structure is filled now as an array of internal nodes, if I now pick any internal node of the tree, how do I know whether the child node of the internal node is an internal node or leaf node ? to do this I am thinking of storing one Boolean variable for each child node to mark it as either a lead node or internal node. But this doesn't seem to me to be a good solution.

Can anyone suggest me a better way to do this ?