Flirting
Many times, flirting is welcome attention. It goes both ways, and both people enjoy it. Flirting doesn't make you feel bad. It's perfectly fine for kids in fact, it's illegal.
Flirting is OK because it can be between two classmates who are both doing the flirting, and no one is being disrespected. But it's not OK for adults to flirt with kids — in fact, it's illegal.