Hi. I have KP, as does my oldest son (7). I asked my dr at about age 30, wondering all my life why I had these little pimply bumps on the backs of my arms and a few on the backs of my thighs. She said it was KP, it is hereditary and there is nothing you can do for it, except exfoliate very well and then mosturize very well. I have had some luck, applying baby oil on my wet skin after exiting the shower. Look it up online, there is a lot of info out there on it and some "home remedies" too. Don't sweat it. I feel bad too I gave it to my little guy, he has a few bumps on his back, face and legs, mostly his arms though. But, I am grateful it is KP and not something that is so much worse!
Editing to add: FOR ADULT SKIN ONLY!
This works for me, to minimize the bumps. I use a pumice stone on the backs of my arms to exfoliate. Then afterwards, use a heavy duty foot cream or vaseline maybe on them. works great!