I have a six year old son who started walking at 12 months and was up on his toes from the very beginning. He was an idiopathic toe walker (that is, there was no reason for this to be happening. He could walk and stand still on his feet but did this rarely in the beginning. No sensory integration disorder, autism or anything else).
We were concerned enough to take him to a pediatric ortho surgeon at 16 months of age (my husband is a doctor so we had access to these consults). He suggested that since my son was just learning how to walk that we get him physical therapy.
We did this for a couple of months- it did not help.
At 2 and 3 years of age, he was still on his toes and we did a second round of PT somewhere else. This did not help. At this point, the original ortho surgeon recommended that we serial cast with subsequent splinting.
With this information, we sought the advice of THREE other ortho surgeons who worked with my husband. They all said to leave it alone.
The last, who was the head of the pediatric department, related to us that his son toe walked, and grew out of it. He recommended we wait until the spring before Kindergarten and then to serial cast if he continued to toe walk.
We were distressed. Our son fell constantly on his face due to his foot position. He was a slow runner which bothered him. In retrospect, I think I was more focused on when he was toe walking than when he was down on his feet. I have photos of him at 2 yrs. running down on his feet. But to talk to me then, I would say this never happened because I was so distressed by it. It didn't help that his preschool teachers were diagnosing him despite my explanations that we had already consulted other professionals (didn't mention to them that my husband and I have medical and advanced degrees in psychology).
At the end, he grew out of it. We saw more and more improvement over the years. He walks normally now. The turning point was five years of age. I switched preschools and placed him in a Montessori School where he was not allowed to wear shoes in the classroom. Who knows if this had anything to do with it, but I remember at this point of his life, that we were no longer reminding him as much about his walking. He finished kindergarten and I am happy to see that the heels of his sneakers are worn down.
I don't think anything we did changed the course of his development. We worried and I understand the worry. It didn't help when people attributed serious issues with our son without having any background to do so.
Good luck with this. Be patient and really try to observe to what degree your little one is up on the toes. Seek the advice of more than one doctor/professional.