The components, bullet, primer and powder will be the same for both .223 and 5.56. However, as stated the 556 is a hotter round and it's warned against shooting 5.56 in rifles chambered for .223. Personally I rather and do have .223 dies. The .223 can be shot in the 5.56 without a problem. Most bolt guns, all that I've seen shoot .223 and not 5.56 so the .223 dies are more useful to me. I doubt you or your son will notice any difference between shooting .223 or 5.56 out of his 5.56 chambered rifle.
Guns are not dangerous! People are! RKBA!