I understand the concern, and I partially agree with you. I have two children and they are not allowed to play violent games or pretend shoot each other. The problem isn't the firearms per say, it is what people are doing with them. If people start stealing cars and going on driving rampages, will we make cars harder to get?
We need to tackle the real problem, America doesn't have a gun problem, it has a violence problem. Let's tackle that problem. Perhaps we could more strictly enforce out current firearms laws. Perhaps we could have stricter penalties for parents whose children use their firearms in shootings. We need to have a REAL discussion though.
These laws are feel good procedures and in no way would stop the atrocities that have happened recently.
As far as the kid making guns, I did it as a child as well. Thank Hollywood for making them cool. Thank the parents for allowing it. If you dislike it, don't teach your children to do it. Have a serious and honest discussion about the real problems with them.