Hi Shannon, I've had kp start showing up since I was 13 or 14. I have over the past few years found some things that have helped me get rid of my kp bumps (I used to get them on the arms and thighs). You should take comfort in knowing that as your little one gets older, they'll be able to keep their kp in check with certain daily routines (plus more and more research is now being done on keratosis pilaris then ever before!)
Since some people see their kp get worse from an undiagnosed allergy to dairy products or gluten, you should try to have your child go gluten free and / or dairy free for a week or two to see if either of these improves the condition at all.
You should find some kids fish oil supplements, yes they make them for kids because the adult ones are huge pills (and some make you have nasty tasting burps). Also, try to limited the amount of
sun exposure and always use a high SPF sunscreen. Also, exfoliate at least twice a day and use a non-greasy moisturizer 3 or more times a day.
Good luck, I really hope this helps!