How old are you?

"Matthew, how old are you?"
"Joseph and Jacob and Mommy."
"How old are you?"
"Joseph and Daddy."

He didn't understand the question. So I made a little song.
"What's your name? It's Matthew. How old are you? I'm two!"

The first few times I sang it he would sing his phrases correctly. If I asked "How old are you?" he would say his same strange answers, but if I sang it he would respond "I'm two!" like the song suggested.

I thought that we had it down. But lately when I've asked "how old are you?" I've gotten a variety of responses.
"I'm three!"
"I'm not two, I'm three!"
"Three! Three! Three!"
"Five!"
"Joseph and Jacob and Mommy and Daddy."

Even when I sing the song, he wants to answer wrong.
"What's your name?"
"It's Joseph."
"How old are you?"
"He's five!"

"What's your name?"
"It's Jacob."
"How old are you?"
"Three months!"

"What's your name?"
"It's Mommy."
"How old are you?"
"You're three!"

And sometimes he just walks around saying, "I'm not two. I'm not two. I'm three! I'm three!"

At this point I think it's just hopeless. After all, someday "three" will be the right answer.