Wanting to get on a plane is voluntary.
I would say an illegal border crossing is often but not always voluntary. Unless things are a lot different in Mexico, I would guess children have little to no say in the matter.
The problem is one side is starting from a bit of a false premise it seems. I just glanced over the bill but it seems you actually have to be doing something wrong before the police can approach you and ask if you are legal. I don’t think they can approach a group of Mexicans playing basketball in the park and demand they all show ID. However, that example seems to be the belief of those against it.
Yes. You do not have to fly I suppose. You can drive. You can walk. You can just stay in your house and become a recluse. But if you wander out into the world you are always subject to being asked for identification. It is a fact of life.