Sure, kids pretend. My kid had this little routine he would do every morning, between the ages of about fifteen months and three years old. "Ask me what I am today!" he would order.
"What are you today?" I would reply. (It was like a little liturgy.)
"I'm a wolf!" he would declare.
Or: "I'm a kitty!"
And then for the rest of the day, intermittently, he howled or mewed or (when he was a lemur) leaped about the room.
Do I need to explain how this is different from being trans?
Because I will.
One is a game. The kid is playing, and you are playing, and we all know it's a game.
A game doesn't cause your child pain. My kid never suffered depression because he wasn't a kitty. He didn't need therapy to understand why he persistently mourned the absence of his kitty body. He didn't require medication because not having a kitty body made him so miserable. He didn't feel, persistently and endlessly and for years, that he was a cat, that this human body was not his own, that this human body was trying to kill him.
Trans is not a kid getting up one morning and deciding they're an attack helicopter, or whatever ever so funny joke you've decided to make about my child.
Trans is the persistent conviction that your body is the wrong gender, often accompanied by crippling dysphoria, or to the point that your life is misery.
If you can't -- or won't -- understand what that is like, then do us all a favor, and keep your bigoted, ugly, ignorant, hate-filled opinion to yourself.
(Also, just FYI, since some of you are apparently unable to do even the most basic research, no one is giving a three year old surgery -- "cutting off [her] dick," as I saw one charming loser put it -- or HRT, or whatever. When we accept our small child's gender, we're talking social acceptance.: social transition. We use the right pronouns. We help them negotiate the world. We don't try to force them to be what they are not, and we certainly don't do that because we have some conviction of what they "really" are.)