If you are going to let your child use your smartphone, tablet or laptop, you'll want to enable parental controls so that he doesn't open applications or visits sites you wouldn't want him to see. Every operating system has different child-protection options. In iOS, you can find the restrictions menu under Settings->General. On Android, you may prefer to install a child-friendly environment such as Kytephone, which only shows certain apps.
Windows 8 and 8.1 allow you to create restricted child accounts, and Windows Phone has a special Kids Corner environment that houses only apps you approve. Both Amazon Kindle Fire and Nook HD tablets also provide restricted modes for kids. Amazon's Kindle FreeTime feature lets you select appropriate content and apps, as well as set usage time limits for your child.