I was contemplating not replying to this question because I have been in a firestorm lately with others on the turtle forums, who without knowledge of reptiles, have kept wild box turtles ( who's populations are also in danger in many areas ).
Many of these people posted similar messages, and it seemed were only looking for emotional reassurance to justify keeping the animal. which I cannot give just to make someone feel better. I'm not saying this is so with you. But consider what is best for the lizard. One of the foremost experts in captive care of horned lizards, Richard Montanucci, advises against any but the very experienced with reptiles keep these lizards, and, I have always agreed. From the time I took on a horned lizard and realized I didn't know enough, eventhough I had many years already with snakes, turtles, and monitor lizards.
To add to that, the SHL species are some of the most difficult to keep alive in captivity. On top of the fact that just horned lizards in general are hard. If you have a few years under your belt with another type of lizard, preferably an Iguana or something similar, I would say you can manage. But, this is just not in the best interest of the lizard in the hands of a beginner, or appropriate as a pet for a child. Unfortunately, it is far more demanding than that.
Mick
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"A man that should call everything by it's right name, would hardly pass the streets without being knocked down as a common enemy." The Complete Works of George Savile, First Marquess of Halifax 1912,246