My niece Svet who will turn four years old this coming May 1 is walking around the house on her tip toes a lot. My sister is bothered by this but Svet is only tip toeing when she is barefooted. She walks very well with her shoes on. maybe it becomes a habit to her so there is nothing to worry about. Our floor is made of tiles and it makes her feet uncomfortably cold when she is not using slippers. She will eventually outgrow it.
In some children toe walking becomes a habit and do it just for fun while there are physical and serious problems associated in kids who tip toe consistently. Kids who have short Achilles tendons makes it impossible for them to walk normally. It can be treated through surgery or stretching/lengthening procedures. Idiopathic toe walking is when there is no physical problem to associate in tip toeing, this is seen in kids with developmental and language disorders.