"switches" refers to the devices that sense and respond to changes in voltage or current. This is an incredibly broad category, encompassing a wide variety of small electronic devices, including cell phones, watches, radios, personal computers, televisions, and many other everyday objects. A switch often has a physical switch on it; however, in some cases, it may have a battery or some type of mechanically operated element that allows the switch to switch off when it's no longer needed. These switches are generally considered safe for use, but should never be used by children without appropriate adult supervision.
In electronics, a switch is usually used to either turn an item on or off. As in a radio or a television, it is also sometimes used to "turn things off" or to switch things on. In the case of the switch being used as part of a circuit, it will often have a wire that connects it to the source that it is connected to, as well as a switch that either turns it on (or off) when it's activated or flips it back on when it's turned off. In some cases, it will have additional functions such as flashing lights, playing sounds or responding to certain signals.
There are times when a child should not use a switch. These are generally outside the range of what a switch should do because a child can simply touch a part of the device they are playing with, causing the device to become damaged. However, it is not impossible to overload a switch, causing it to short out, for example, or cause it to activate when it shouldn't. In these cases, it is generally safe for a parent to leave a child alone to play, even if the parent knows there are potentially dangerous elements within the switch. It is never recommended to leave a child unsupervised in a room that contains electricity. Remember, when in doubt, always consult a qualified electrician before using any electrical device of this nature.