Children can be quite clumsy with technology, especially the younger ones. By mistake, they can access all kinds of settings and options on your iOS device, possibly deleting or changing all kinds of data. Do you have photos or videos you'd like to keep forever? Better have a backup if you leave your device unattended with your kid, or you might come back and find all of it deleted! That's why more and more iDevices and Android phones have a Kid Mode that lets parents put restrictions as to what their children can access on the phone or so that they don't turn off a game/cartoon played on the phone by mistake.
On iPhone, iPad and other Apple devices this mode is called Guided Access. It lets you limit your child to a single application, and even control what features can be accessed in the app itself. If your kid is a bit younger, it's easy for them to poke the screen and access ads seen during gameplay, or turn off a YouTube video with their favorite cartoon. Not to mention the beloved Home button, seen in some of the older devices, kids absolutely love to click it, so unless you turn it off, no game or cartoon will stay on for long!
First of all - please remember, Guided Access is a lock focused on a single app, so you might need to change some settings for different software, depending on if it's a game, cartoon or a music player.
Once done, your device will be locked into the application. Pressing the Home button or swiping up doesn't leave the app, so there is no chance for your child to do anything by mistake. You'll see a message at the top of the screen that Guided Access is enabled. Press the Home button or the side button three times to enter the passcore and exit Guided Access.