So many boundaries are hard for our kids. They can be the simple ones like not getting into another person's personal space. My oldest adoptee, Lexy, was always in everybody's else's personal space. This kid would bump into siblings many, many times a day. She simply did not know how to walk without bumping into another person. Today, after many years, she is able to walk with appropriate personal boundaries. Was there a need for sensory imput? Not really. Lexy didn't know how to get appropriate touch, so she bumped into people all of the time.
This problem with her also manifested itself with strangers. She would sit in anyone's lap. We soon had to make it an absolute rule that Lexy sat in no one's lap, except parent's. It took years before she could comply. People that should have known better didn't know what to do when this big kid climbed into their lap. Once again, it stopped. It took years.
I'm not sure what the reason for such issues are. Many would say RAD, which so many kids have in varying forms. Many say FASDs. They certainly contribute. Early sexual abuse is a huge problem with maintaining appropriate boundaries. Trauma in general contributes. All of our foster/adoptive children have almost all of these simultaneously. It takes years and years of modeling appropriate behaviors for them to unlearn. Lexy was hugely traumatized as a young child for many years. Pre-natal exposure disrupted the pathways in the brain. She will never have typical boundaries, but she is improving yearly and that's all we can ask for with anyone.