Girls. When we go out for a walk with my daughter, she is afraid of ot…

Girls. When we go out for a walk with my daughter, she is afraid of other children on the playground. When they approach her, she starts crying immediately and I feel like it's going to be hard to calm her down. She even gives them her toy and runs straight to me. How can I teach her to socialize? I think it's because she's always sitting next to me 24/7. She doesn't even talk to grandmothers on the phone.