I might know just what you are talking about. I also used to walk on my "toes". This was somewhat due to having had Osgood Schlatter's disease as a child, which left me with bi-latteral patella-alta, which has led to chondromalatia and osteo-arthritis. The other reason being that I have flat-feet.
The short version of this, is that I was walking on my toes because:
1. I was trying to gaurd my knees from having to go into full extension and in doing so avoid dislocation.
2. I have flat feet and turn my feet in as I walk.
You might want to first see a pediatrist to evaluate your stance/walking and check for flat feet. I have recently gotten inserts for my shoes to compensate for my flat arch and it helps a lot. More interesting however, is even though I am now walking "properly", I now have the sensation of walking on my toes while actually walking with my feet flat. That suggests that you might be having the sensation of "walking on your toes" while in fact, that is how you would feel if the arch of your foot is correct, which would allow your heel to touch the ground while walking.
If the pediatrist can't find anything wrong, you might want to see a knee specialist and get your knees evaluated for any abnormalities.
I hope this made sense