Building robots can be a great past-time for older kids and adults alike, and many families find it to be a fun activity they can do together. Of course, building robots is also a lucrative industry, and some people find advanced careers springing out of their hobby. There are a number of hobby groups dedicated to building robots, and an entire cottage industry has sprung up around providing kits for building them, as well as books and workshops dedicated to the craft. As with any electronics endeavor, it is best for children to have some sort of adult supervision before they set off building robots on their own, as they can be dangerous if handled improperly.
Before you start building robots on your own, you'll want to decide what you want to build them for. If you're just interested in building robots because they look neat, then you can build much simpler robots and focus more on the aesthetic properties of them. If, on the other hand, you're interested in entering robot battle competitions, you'll have to spend quite a bit of time testing your robots and making sure they can compete well. You may also just be interested in building robots to teach you more about electronics and basic machine learning, skills that can help you if you continue to pursue electrical engineering and robotics.
Setting out to build your first robot is an exciting endeavor, but it is also likely to be a frustrating one. Building robots is not an easy task, and it can take a great deal of trial and error before you figure out what works and what doesn't. When first starting out, try to set your sights fairly low. Start with a simple robot design, to teach you the fundamentals, and make sure you are comfortable with the tools and supplies you'll be using. If you set your bar too high initially, you may wind up with a failed project and no end of frustration, which may dampen your interest. Don't worry, you'll have future projects, so start out small for now, and use the knowledge you gain to figure out what you want to try next time around.
To begin with, you'll probably need some money to invest in supplies. While later you may be able to build a robot for very little cost, in the beginning you'll likely have to rely on at least some kit parts, as you won't have spare parts just lying around. You'll also need some place to build, and unless you have an electronics shop, you'll want to join a local electronics club, or ideally a robotics club. These may be free, or they may require regular dues, but in return you get to use their space and their supplies, as well as the incredibly useful resource of having access to other roboticists.
You can find designs for your first starter robots online, and there are a number of resources that can give you tips how to get started. You can also find affordable starter kits, which come with all the parts and instructions, and can help you get an idea of the basics of building robots. Ultimately, if you stick with it and keep progressing in incremental steps, you'll eventually be building complex robots able to do tasks, move over difficult terrain, and even engage in combat with other robots.