Every human being is important. What you probably mean is why does government and educational institutions favor children, over adults. The answer is very obvious.
Children are vulnerable and they can not take care of themselves. A child without guidance, can not make it on his own.
The life of an adult person is always influenced by their childhood. Almost every single human being in the world has been shaped due to their upbringing. The decisions that adults take every day in their life has to do with their childhood. It has been psychologically proven that people are affected by their experiences as a child. What they imitate as adults is usually something they saw in their childhood.
People who were traumatized by a horrible event in their childhood grow up to be scared, nervous, they sometimes need therapy, they can be unstable.
Educational mediums and government organizations know that, and they try their best to bring a safe upbringing to children. Which is, in a lot of cases, deterred by the parents and their decisions. So the system is not perfect, but that's the whole principle of the idea why children seem to be more important that adults when it comes to government help.
Lately a large number of parents are drinking and using drugs which can affect their children and the outcome of their lives as adults. It's a sad situation.