Twins
noun
The pair of children are the same as each other. They're twins.
The reading is like 二人, (the ふた part) plus 子, combined together. A little weird, but makes sense. Watch out for the rendaku.
「男の子ですか？女の子ですか？」「実は双子の男の子なんです。」
"Is it a boy or a girl?" "They are actually twin boys."