Okay, I have these two kindergarden and 1st grade friends that are girls that made out! Idk what to do! Help?

I have these 2 friends that made otu. I'm concerned because they're really young . . . They live VERY close to me and I don''t know what to do. The one in first grade told me that they had a sleepover and her kindergarden friend woke her up in the middle of the night and asked her if they should kiss. Ewww. She said yes beccause she didn't want to hurt the kindergartener's feelings. She also told me that they kissed on the lips and cheeks, and also put down they're pants and licked they're cheeks. This is SO nasty! She told me to keep it a secret, but idk what to do. What should I do? I'm a fourth grader and they're way younger than me, so idk what to do! Help!