How to tell my younger sister ?

My sister is in 3rd grade and is extremely innocent.....so today I went to pick up her from school on bike....and from far I saw some chapris on a duke 125 staring at her awfully.....and I twisted my throttle all the way.....when I saw one of them saying something to my sister.......then the loud exhaust note from the bike maybe scared them.....they got away.......

I asked my sister.... whatd he say ?.....shes like he asked which class I'm in and my name.....and this clueless innocent girl answered both......

How do I explain her the evil of this world and info about creeps and stuff bout how many men are ? I literally don't know......How ud do it if u were me ?

In my case too since childhood......It took me long to understand evil and people CAN BE bad stuff.....

Note : obviously shes told the basics like don't talk to strangers..... don't answer but shes a child she don't seem to remember