Be legitimately afraid. Welcome to the club. We have endless choices of what we can watch. But what we watch does have an effect on us in one way or another. With children the lines between fantasy and reality are especially blurred as they watch TV or videos.
Children act out what they see, children repeat what they hear.
As parents we often choose with our remote control what behaviors our children will copy and what they will add to their vocabulary. So you're a parent who can't quite stand how syrupy and outrageously optimistic Barney is. It makes you ill. Welcome to the club. But take a look at the alternative children's programming and ask yourself if that's what you want your kids to emulate.