I worry my child doesn't realize when they're being teased or taken advantage of.

Not noticing teasing or being used is often because reading others' intentions is hard, or the feeling of "I'm glad to be included" comes first. Start by conveying with concrete examples that "a real friend doesn't force you to do things you dislike or make fun of you," and decide on an adult (parent, teacher) they will always tell when something feels "off." Teach warning signs such as handing over money or belongings, or being given a different role only for themselves. Share information with the preschool/school and have them watch during times with less adult supervision, like breaks. If bullying is suspected, consult the school early.