Is it normal for a child to have a crush on a teenager?

Ok I have these neighbors who look after their granddaughter pretty much all day every day when her parents are at work. I found this piece of paper crumpled up on the sidewalk wrapped in rubber bands. It said "Nick you are so *smiley-face. Guess who?" I'm not gonna lie I'm really creeped out but kinda pissed off cuz everytime she sees me she says hi and I just want her to leave me alone. I know she has this major crush on me for a few years, but I just think its creepy for a 1st grader to have a crush on an 18 yr old. Is this normal and am I overreacting?