My now 4-year old also fractured her tibia when she was 2½. It took me 2 weeks and several doctors, emergency rooms, etc for them to finally find the problem. When we finally got to the pediatric orthopedic he found the fracture. He gave me the option of either cast it or not. After thinking long and hard we decided to go with a bright pink full-leg cast. I felt awful, but he said it would heal quicker and I felt she would be in less pain. We had already had 2 weeks of trying to rest it and I was afraid it wouldn't heal correctly. She was already walking sort of wierd and she had been through so much. She did great with the cast, she had it for 8 weeks. She had a walking shoe and was able to walk on it the same day we got home. She was unsure of it at first but learned quickly how to work around it, kids are sooo resilent! It was in the middle of the summer and very hot and bath time was interesting, but she never complained and went back to daycare and did everything she normally did. She never had PT and she is doing fine today. It was a little uncomfortable and strange the first day or so without the cast and of course weak. Considering the situation, the cast was a good experience, I'm glad we did it. We have really cute pictures and of course she talks about it when she sees them, but never anything negative towards it.
Good luck. I know first hand what a hard time and decision it is for you. It's not near as hard on them as it is for the mommies!!