Hi,
A reptile is not an appropriate pet for a child, and especially not a juvenile MHD, firstly.

The dragon sounds stressed and off temperature, and/or sick, and it sounds like you did not do research on the animal before purchase.

A UVB bulb is not "blue". You need a couple of fluorescent strip lights for this animal which specifically state "UVB" on them, or better yet, a mercury vapor spot lamp, such as a Mega-Ray SB100, or T-Rex Active UV Heat. He is not getting anything with the blue and red incandescent bulbs you are describing.

You may be feeding improper prey size for this animal's youth, and he may either refuse food, or you could kill him with crickets that are too large through impaction and gastroenteritis. Use age appropriate prey that is no more than 1/2 the length of the lizard's head, and 2/3 the width.

There may be parasites, as no matter where you got him from, there is a chance that he is wild caught, or his parents were. It is still simply too cheap for people to import wild captured rather than spend the money on setups to breed.

Your temps sound to be off to from the description of his color change. And you did not state what humidity levels you are keeping. All this being moved about, lack of UVB, along with other possible problems, will cause stress; and stress kills reptiles.

If this dragon looks sick to you, and you don't want it to die, then step up and take it to the vet as you should. That's simple enough.