Okay kiddo, design for all or inclusion means making things in a way that everyone can use and enjoy them, no matter what their abilities or disabilities are.
For example, think about a playground. What if there were no swings or slides for kids who use wheelchairs? That would not be very fair, right? So, designers make sure there are special swings and slides that those kids can use too.
Designers also make sure that things are easy to see, hear or understand. Like, they use big letters and pictures in things like signs so that people who have trouble reading or seeing can also understand it.
It is like when you have a party and invite all your friends. You want to make sure that everyone has fun, not just some people. You want everyone to be able to play and enjoy the party together, that's what design for all is all about!