Five Nights at Freddy's is all about heart-pounding jump-scares. It's rated 12+, so it's not quite suitable for many preteen players. That said, the series forgoes the blood, gore, and violence typically associated with the horror genre in favor of innocent (if still pretty terrifying) shocks.
Moreover, if you have a lot of freetime, let's take a look at many other hot games such as:
Retro Bowl Unblocked,
Stumble Guys 2 Unblocked...