That is a child with brain cancer. At his age, many children wish to be things they perceive as being heroes. Also children at his age, if they are raised in a protected environment, will not be aware of all of the various forms of problems our people go through. They are sheltered from the ills of society, the racism, the evils our government participates in, etc.
I say all of that to say that child should not be receiving all of this vitriol from some of you. He is a child who may not even be here much longer and any parent that loves their child will seek to grant a possible last wish in that circumstance. The anger you have for that child is misplaced, and should be solely placed on Trump and his Administration for making it a political stunt.