For generations, young people all over the world have taken an interest in social justice and found the courage to fight for their own rights and the rights of others. Here are four inspiring middle grade books that prove you’re never too young to stand up for what you believe in and make a difference.

This series follows 11-year-old Parvana, who lives under Taliban rule in Afghanistan. When her father is arrested and her family is left without someone who can work or even shop for food, Parvana, forbidden to earn money as a girl, disguises herself as a boy to help her family survive. The Breadwinner is an empowering tale with a sharp and brave heroine.

Stella lives in the separated south in 1932. Out, late one night, wandering around, Stella and her brother witness a Klu Klux Klan activity, starting an unwelcome chain of events in her otherwise sleepy town. With a compelling and courageous voice, Stella tells the story of how she and her community ban together against racism and injustice.

When Julian is sent to stay with his disinterested aunt and uncle for four months, he discovers that his Uncle’s corporation plans to cut down a group of redwood trees at Big Tree Grove and decides to take a stand to save the trees. Perfect for the young environmentalists in your life, Operation Redwood is an adventurous tale as Julian and his friends hatch scheme after scheme to save these giants of nature.

For more mature readers, this unforgettable autobiography tells the true story of Nujood Ali, a ten-year-old Yemeni girl married off at a young age, who decides to resist her abusive husband and get a divorce. A moving tale of tragedy, triumph, and courage, Nujood’s brave resistance has inspired generations of women and young girls.

Middle school is challenging for so many reasons — academics become more difficult, schedules fill up with activities, and, in what might be the most challenging region for kids and parents alike, friendships change. Friendships change over time, not just because our children evolve, but because the very nature of friendship evolves with them. The best parents should learn to let go so that their children can succeed in their tween friendships.

Early in childhood, our children’s friendships arise out of closeness and habit. We throw our kids into the sandbox with our friends’ kids, and this arrangement works for everyone. As kids get older, however, they begin to build emotional connections with friends based on similarity. Their shared interests, dreams, and goals begin to edge out mere convenience. When they become tweens, friendships become much more complex, and for good reason. Tweens use friendships as a way to try on an identity. They begin to build friendships based on new priorities.

All too often, the shifting sands of tween friendship result in broken hearts. Tweens feel abandoned and betrayed as friends move back and forth between comfortable old relationships and exciting new ones. As any parent knows, our own personal heartache hurts, but the secondhand heartbreak we experience through our children is much more painful, mainly because it’s out of our control. The urge to meddle, to save and heal, is powerful, and while meddling around in tween social contact may make us feel better, we must stay out of it.

Tweens move from relationship to relationship, adopting this detail of a friend’s personality,abandoning that characteristic of another, until they have collected the essential elements of their identity. Some relationships will survive this process, and some will not, but everyone is an important phase of the journey. We may not love every outfit our tweens try on, but it’s our job to be there when they emerge from the dressing room, when they do a little twirl and wait for us to tell them how grown up they have become.

By now it’s almost common knowledge that spending time in nature is good for you. Areas with more trees tend to be less polluted, so spending time there allows you to breathe easier. Spending time outdoors has been linked with reduced blood pressure and stress, and seems to motivate people to exercise more. So it’ll come as no surprise that there's research showing that spending time in nature is good, which has been known for thousands of years. There’s dozens of papers showing that.

University of Exeter Medical School researcher Mathew P. White said “We get this idea, patients are coming to us and they’re saying, ‘doctor, how long should I spend?’and the doctor is saying, I don’t really know.” So White and his team decided to find out by using data collected from nearly 20,000 people in England through the Monitor of Engagement with the Natural Environment Survey. And their answer? Two hours a week. People who spent at least that much time-either all at once or totaled over several shorter visits-were more likely to report good health and psychological well-being than those with no nature exposure. Remarkably, the researchers found that less than two hours offered no significant benefits.

So what’s so special about two hours? “ I have absolutely no idea. Really. We didn’t have an apriori（由因及果的）guess at what this would be. It emerged. And I’d be lying if I said we predicted this. I don’t know.” Even more noteworthy, the two-hour benchmark（基准）applied to men and women, to older and younger folks, to people from different ethnic backgrounds, occupational groups, socioeconomic levels and so on. Even people with long-term illnesses or disabilities benefited from time spent in nature—as long as it was at least 120 minutes per week.

While the findings are based on a tremendous number of people, nobody knows why or how nature has this benefit. “I want to be really clear about this. This is very early stages. We’re not saying everybody has to do 120. What research do we need to take this to the next step before doctors can have the true confidence to work with their patients? But it’ s certainly a starting point,” White said.

As for child vaccinations, parents usually get paperwork lost, or forget whether their child is up to date. Now a group of MIT researchers has developed a new way to address this problem: inserting the record directly into the skin. Along with the vaccine, a child would be injected with a bit of dye that is invisible to the naked eye but easily seen with an app that shines special light onto the skin. The dye would be expected to last up to five years.

The system would provide quick and easy access to vaccination history, and add little to the cost or risk of the procedure. “In developing countries where medical records may not be as complete or as accessible, there can be value in having medical information directly associated with a person,” says Ana Jaklenec, lead author of the study.

Delivering the dye required the researchers to find something that was safe and would last long enough to be useful. “That’s really the biggest challenge we overcame in the project,” says Jaklenec, adding that the team tested a number of dyes hut could not find any that lasted when exposed to sunlight. The team ended up using a technology called quantum dots, which were originally developed to label cells during research. The dye has been shown to be safe in humans.

“When people were still getting vaccinated against smallpox, they got a visible scar on their arm that made it easy to identify who had been vaccinated and who had not. But obviously, we didn't want to give people a scar.” Jaklenec says, noting that her team was looking for something that couldn’t be seen. The researchers also wanted to avoid technologies that would raise even more privacy concerns, such as databases with names and identifiable data.

The researchers hope to add more detailed information to the dots, such as the date of vaccination. Along with them, the team eventually wants to inject sensors that could also potentially be used to track aspects of health such as insulin levels in diabetics.