1. Sanctions wouldn't do much because China is pretty much the only one who will trade/sell with N. Korea. Other countries, including the US, send money for humanitarian reasons even though they know that the money never gets to those in need.
2. Pyongyang is practically a sealed off city. They are the military and elite who have everything they want. Food, clothes, job. They owe pretty much everything to their leader, so if they were to rebel against Kim Jong-un they would likely be seen as traitors. N. Korea has had three generations of indoctrination - that is not easily overcome by people whose lives rely on being loyal to the dictator.
Those outside of Pyongyang barely have food and clothes and a place to live. They eat grass and many abandon their children at a young age because it tears them up that they can't feed them. The remaining population are still living in concentration camps. They are also up to the third generation of families born and still living in the camps - along with others who are sent to the camps if someone swipes a kernel of corn from a field or something. It doesn't take much. I've read two books on this by insiders who escaped. Look it up.
3. China stands to lose money if they stop trading with N. Korea. But they also are doing so with their eyes wide open - they aren't stupid about what is going on inside the country. I don't think anybody would begin a war except for N. Korea, therefore we don't have to worry about China. We are allies with them as well. If anybody were to ally with N. Korea, they would do practically all of the fighting because N. Korea would run out of all military supplies in a minute compared to the rest of the developed countries in the world - let alone all of these countries working together against N. Korea.
4. I also agree that their missiles wouldn't do much and they probably don't have many. Compared to us and other developed countries they wouldn't have the amount or power to do much. They would be wiped off the globe if they started something. Kim Jong-un is said to be crazier than his father and grandfather. But his health also stinks pretty bad from so much overindulgence.
5. What can we do? As kids (or even adults without political/military power) there isn't much we can do.
---We can try to be informed on the matter because I think that would help us to feel better about things, not worse. That would include learning about the history of N. Korea. I read that in Pyongyang, kids are made to read The Diary of Anne Frank. Not unusual you say? It is because they teach that she and those hiding with her were cowards and fools, etc. whereas we believe the opposite. Just don't buy into the propaganda that some news outlets put out from time to time with photos. Whenever they are let into the country they are always together with leaders and interpreters. They can't go anywhere without them. They go to the things that are put on just for them and can't even get anywhere close to being outside of Pyongyang to see how the rest of the country lives.
---We pray for those in Texas - we need to also pray for safety from N. Korea trying to begin a war by taunting countries. Also, if you are a believer, ask God to give you peace. We can have peace even in the most trying times if we look to him.