Always use complex, unique passwords for each website you visit.
You can learn more about how to create strong passwords and how to manage them here. Password managers makes things easier: Unique passwords are key.
Most sites do not have a way to keep the wrong kinds of people from signing up, making dating sites very kid-unfriendly.
A child should not be engaging in parts of the Internet where they would get approached by adults looking for a date.
In the world of internet, numerous apps have been developed for hooking up and finding a partner for oneself.