Do a lot of children get stressed?

Yes. Life, and it's trials and tribulations, is stressful. Kids need to learn how to be able to handle stress without decompensating. We can guide our kids and provide unconditional acceptance, but we cannot undergo the stress for them. Kids need to learn how to sooth themselves and not rely on the satisfaction of others to feel good. Peer pressure can be fierce.
Yes. Stress is common to children, and it can be a problem with children who tend to be sensitive and easily affected by their environment and situations.