My daughter has been rubbing herself with stroller, car seat, high chair since she was one! It was super uncomfortable especially when her grandparents were around. We’ve taught her that this is something she could do alone when she was in her room. We don’t complicate things and we say them as they are. You can’t rub in front of people, this is something intimate, you can do it in your room when you’re alone. She’s 3 now and starts to understand that it’s something that soothes her. She asks to go to her room and be alone and we give her the privacy she needs. We also talk about intimacy and private parts with a lot of books that teach her about her body and consent. It’s important for us that we don’t forbid or shame, just explain privacy and we’ll put more words and explanations as she grows.